Pitch-Specific Advanced Analytic and Pitch-Tracking Risk Factors for Ulnar Collateral Ligament Injuries in Major League Baseball Pitchers

Abstract

Background:

The utilization of new pitch-tracking metrics has driven player development and provides more predictive pitch-specific data on physical characteristics and performance. Given the differences in each pitcher’s arsenal, these pitch-specific metrics provide new potential variables to investigate ulnar collateral ligament (UCL) injury risk.

Purpose:

To evaluate the association of several pitch-specific advanced analytic and pitch-tracking metrics on UCL surgery rates in Major League Baseball (MLB) pitchers.

Study Design:

Case-control study; Level of evidence, 3.

Methods:

We performed a retrospective case-control study on all MLB pitchers who underwent primary UCL reconstruction or repair from April 2018 to November 2023. Exclusion criteria included pitchers without 2 qualifying seasons of preoperative pitch-tracking data or who previously underwent UCL surgery. Matched controls were identified in a 2:1 manner by using season, age, position, handedness, and pitch count as covariates. Pitch-specific advanced analytic and pitch-tracking metrics used commonly in the evaluation of MLB players were collected from public web sources sponsored by MLB. Statistical analysis consisted of unpaired t tests comparing preinjury metrics between the case and control groups, along with binary logistic regression.

Results:

A total of 115 MLB pitchers who underwent UCL reconstruction or repair were compared with 230 matched controls. Increased velocity for fastballs, changeups, and sinkers were all associated with UCL surgery. A decreased horizontal release point for fastballs, curveballs, and sinkers were also associated with UCL surgery, along with an increased horizontal approach angle above average for fastballs and sinkers. An increased spin rate for sliders and an increased release extension for cutters were also associated with surgery. Large statistically significant differences in Pitching+ and Location+ for fastballs, changeups, and sinkers, and in Stuff+ for changeups, were associated with surgery. There were no differences in pitch-specific pitch count, active spin, spin axis, vertical release point or approach angle, or overall pitch movement between cases and controls. Binary logistic regression showed that higher velocity fastballs, sliders, and changeups were all associated with UCL surgery, along with sliders with a higher spin rate and cutters with a longer release extension.

Conclusion:

This study demonstrated that pitch-specific associations with UCL surgery exist compared with matched controls. Specifically, higher velocity fastballs, sliders, and changeups were all associated with UCL surgery, along with sliders with a higher spin rate and cutters with a longer release extension. Fastballs, changeups, and sinkers with superior ability (Pitching+) and command (Location+) were also associated with UCL surgery. While fastball velocity appears to play a role in the rise of UCL injuries, recent trends in decreased fastball usage and improved secondary pitches suggest that an increased focus on entire pitching arsenals is warranted. This study investigated a number of pitch-specific advanced analytic and pitch-tracking metrics as potentially new variables to assess UCL injury risk.

Keywords

ulnar collateral ligament injury thrower’s elbow Tommy John surgery advanced analytics Major League Baseball fastball

The rate of elbow ulnar collateral ligament (UCL) injuries continues to rise and remains a primary concern, threatening the careers of Major League Baseball (MLB) pitchers.^18,34,41,44 This is despite the significant financial implications for both the player and team, along with an increased emphasis on injury prevention in recent years.^24,27,29,42 This includes new pitch count guidelines for baseball pitchers at various competition levels.^24,42 Despite these efforts, the number of UCL injuries continues to mount, suggesting that other factors may be contributing to their rise in MLB pitchers.

Since 2017, MLB began releasing new pitch-tracking and advanced analytic data derived from high-resolution camera systems installed in every MLB stadium. These systems (Trackman and Hawkeye) now record essentially all batted balls and provide more detailed information such as spin rate and axis, release point, approach angle, and movement in multiple directions for each pitch in a player’s repertoire.^1-3,12,35,39 Other analysts have recently developed new advanced analytics such as Stuff+, Location+, and Pitching+, which were designed to provide a more objective metric to evaluate various aspects of a pitcher’s ability that have not been previously described.^22,28,40

These data also provide potentially new variables that can be used to assess UCL injury risk, allowing for potentially more targeted prevention protocols to be developed. While many studies have looked at traditional measures such as velocity, pitch type usage, pitch count, and demographic factors, few studies have investigated the relation of certain pitch-tracking data to UCL injury rates.

There have been 2 recent studies that looked at pitch-tracking metrics: one evaluating return to performance after UCL surgery and another reporting on metrics associated with UCL surgery from 2017 to 2023 in a matched case-control series.^25,26 While they found that pitchers who threw harder with less fastball usage, and had superior overall pitching ability (Pitching+) and strike-zone command (Location+) were more associated with having UCL surgery, their analysis lacked pitch-specific data. Reporting pitch-specific data requires even more comprehensive analysis than what has been previously reported, and there is an overall lack of understanding on pitch-specific risk factors for a UCL injury. Given the differences in each pitcher’s arsenal and pitching trends that favor certain pitches and movement profiles, it is critical to determine which pitch-specific characteristics lead to an increased risk of injuries, which in turn may influence player training protocols.^{5,7,22,33,34,44}

Therefore, the primary objective of this study was to evaluate the association of pitch-specific advanced analytic and pitch-tracking metrics on UCL surgery rates in MLB pitchers. Our secondary objective was to analyze the effect of large year-to-year changes in these metrics, providing insight into how rapid improvement may influence UCL surgery rates. Our hypothesis was that there would be pitch-specific differences between those who underwent UCL surgery and those who did not. Overall, we hope that this study better informs players and teams on safe player development protocols.

Methods

Study Design

Our study was deemed exempt from institutional review board approval as not constituting research on human participants under 45 CFR 46.102. We conducted a retrospective analysis, using entirely public data, on all MLB pitchers who underwent primary UCL reconstruction (UCLR) or UCL repair from April 2018 to November 2023, as described in previous studies.²⁶ Exclusion criteria included pitchers without 2 qualifying seasons (ie, >100 pitches in a calendar year) of preoperative data or who had previously undergone surgery on their UCL. Analysis of active spin, spin axis, Stuff+, Location+, and Pitching+ did not require 2 qualifying seasons of preoperative data because of power limitations, given that these metrics have only been available since 2020. A total of 144 MLB pitchers were identified with UCL injuries requiring primary UCLR or UCL repair from April 2018 to November 2023 using a public database,^26,37 which has been used previously in other studies and cross-referenced with public websites and official press releases.^10,34 Of these pitchers, 29 were excluded from our study based on the above criteria. To qualify as an MLB pitcher, players must have had at least 10 innings pitched in MLB during the index season or the year before the injury. Baseball Savant (www.baseballsavant.mlb.com) and Brooks Baseball (brooksbaseball.net) were used to collect pitch-tracking data obtained through high-resolution camera systems implemented by MLB, similarly to previous studies.^3,4,26

Data Collection

Data from camera systems set up by MLB in each stadium were compiled and then released for public use.^2,14,36 Participant data including whether the player was a starting or relief pitcher were collected from well-regarded public websites such as FanGraphs and Baseball-Reference and stored on an Excel spreadsheet (Microsoft). FanGraphs wins above replacement, expected fielding independent pitching, and skill-interactive earned run average were also recorded. Stuff+, Pitching+, and Location+ began to be recorded in 2020 and are available on FanGraphs; a score of 100 roughly grades out as league average relative to other similar pitches.^14,28,39 To increase our power, analysis of Stuff+, Location+, and Pitching+ did not exclude pitchers who had less than 2 qualifying seasons of preoperative data. Each of these variables is defined in Table 1.

Table 1

Commonly Used Advanced Analytics in MLB^a

	Definition
FanGraphs WAR	This is a cumulative statistic that measures a player’s value in all facets of the game by comparing how many more “wins” he is worth to a team than a replacement-level player, who is a readily available minor leaguer or a free agent. Previous reports have considered 1 WAR to be equivalent to nearly $7 million in payroll value for pitchers, with an even greater value per WAR as a player exceeds over 2 WAR in a season.^7,26 It is impacted by the amount played and is named after the developing organization.
Expected fielding independent pitching and skill-interactive earned run average	These are rate-based statistics that aim to measure what a pitcher’s earned run average would be after standardizing for the strength of defense, ballpark factors, and other possible confounding variables. They are not impacted by the amount played.
Stuff+	Stuff+ evaluates the physical attributes of a pitch such as velocity, vertical and horizontal movements, approach angle, and release extension. The most effective pitchers in MLB tend to grade out high in Stuff+.¹²
Location+	Location+ is a count- and pitch type–adjusted measure of a pitcher’s ability to place pitches in the right location, better known as command. Location+ looks at average locations of a specific pitch on a specific pitch count and assumes that the pitcher’s intent is generally the same across the league. Command is critical for success and is often what distinguishes the elite pitchers. It is currently unknown whether pitchers regain command (Location+) after UCL surgery.
Pitching+	Pitching+ uses the physical characteristics (Stuff+), command (Location+), batter handedness, stadium, and count of each pitch thrown to assess overall pitching ability. Pitching+ also captures the effect of pitch sequencing to set up and confuse hitters for future pitches, such as changing eye levels by throwing a high fastball, followed by a low-and-outside slider. Therefore, Pitching+ may also capture the mental process and execution of a pitcher that are otherwise difficult to evaluate, and it has been shown to be a strong predictor of future success.²

Stuff+, Pitching+, and Location+ are all scaled similarly to intelligence quotient; a score of 100 is graded out as league average. MLB, Major League Baseball; UCL, ulnar collateral ligament; WAR, wins above replacement. Table reproduced with permission from Mastroianni MA, Kunes JA, El-Najjar DB, et al. Advanced analytic and pitch-tracking metrics related to risk factors for UCL surgery in Major League Baseball pitchers: a case-control study. Orthop J Sports Med. 2024;12(12):23259671241302432.

Mean velocity, fastball velocity, horizontal and vertical movements, approach angle, release point, and release extension were also obtained for each season from Baseball Savant.^3,5,6 If pitchers threw multiple different fastballs (4-seam vs 2-seam), pitch-tracking outcomes were recorded for the more frequently used fastball. Spin rate, active spin, and spin axis were also collected and are defined in Figure 1. Analysis of active spin and spin axis also did not require 2 qualifying seasons of preoperative data given power limitations.

Release extension, horizontal and vertical movements, release point, and approach angle were tracked from the catcher’s point of view and are defined in Figure 2. This means that a right-handed pitcher’s horizontal release will be toward third base, representing a negative value, while a left-handed pitcher’s horizontal release will be toward first base, representing a positive value. Horizontal movement can be either positive or negative as different pitches can move toward or away from the batter. Vertical movement can also be positive or negative, with positive values indicating a pitch that resists gravity more and “stays up” compared to the expected location of the pitch secondary to gravity alone. This is usually secondary to backspin, and with recent pitching trends is more typical of high-spin fastballs that produce this “rising effect” to make it more difficult to hit. Negative values indicate a pitch that drops more than expected secondary to gravity alone, and is typically a result of backspin most commonly in breaking pitches such as curveballs and sliders. Approach angle is a function of the pitch’s release point (starting location), final location, and velocity and acceleration vectors in all 3 dimensions, which ultimately determine the pitch’s movement through space.⁵ Because release point can be altered simply by a pitcher’s position on the mound relative to home plate, horizontal approach angle (HAA) above average and vertical approach angle above average normalize for location, handedness, and release point for each pitch type. These values may be zero, “minus” values indicating sharper angles toward right-handed batters, and “plus” values indicating sharper angles toward left-handed batters.⁵

To simplify this, all horizontal metrics were normalized for pitcher handedness, similar to previous studies.^10,26,34 Although horizontal movement can be positive or negative, we used absolute values instead of relative values, given that positive or negative horizontal movement is determined by batter and pitcher handedness, which would confound our analyses. Given that vertical movement and approach angle above average is not impacted by handedness, positive or negative values were included.

The date of surgery was used as the index date for data collection; the calendar year immediately before surgery with a pitch count >100 was designated as T1, the year before that was designated as T2, and the year before that was designated as T3. Pitchers who started in ≥50% of games for the T1 season were identified as starting pitchers, and pitchers who started in <50% of games in the season before UCLR were identified as relief pitchers.

Control Group

Players matched 2:1 by season, age, position, handedness, and pitch count were selected as a control group, similarly to previous studies.^10,26,34 Controls were selected first by index year of surgery as the matched pitcher in the UCL injury group. Next, position (starting or relief) and handedness, followed by age and the most comparable number of pitches in the index season, were used to generate our matched control group. For pitchers who were hurt in the off-season, data from the year immediately preceding the injury with >100 total pitches thrown were used. Any pitcher with known previous primary UCLR, primary UCL repair, or platelet-rich plasma injections in the UCL was excluded. Descriptive and pitch-tracking data for the control pitchers were collected in the same way as for the UCL injury group.

Statistical Analysis

Statistical analysis was conducted, similarly to previously described studies.²⁶ Unpaired t tests were used to compare continuous variables between the cases and controls, while the chi-square test was used to compare categorical variables. Changes in the 2 or 3 seasons before the injury were also analyzed to see if large season-to-season changes were independently associated with UCL surgery. Binary logistic regression utilizing data from the season before surgery was conducted to determine pitch-specific metrics associated with an injury and to help eliminate confounding, given the large amount of variables included in our unpaired t tests. Our judgment was used to exclude certain variables related to each other and that were underpowered (Stuff+, Location+, and Pitching+). Splitters were omitted, given the low sample size (n < 30). Additionally, 95% confidence intervals were calculated for each variable in logistic regression. Multiple pitches could not be included in the same logistic regression analysis, given the differences in pitch arsenals among the included pitchers (eg, not every pitcher throws the same pitches) and to not dilute our analysis. All data analyses were performed using R statistical software (R Project for Statistical Computing), Excel for Mac (Microsoft), and SPSS (Version 26; IBM). Statistical significance was set at P < .05.

Results

A total of 115 MLB pitchers who underwent primary UCLR or UCL repair were compared with 230 matched controls. The mean age was 27.9 ± 3.3 years for cases and 28.4 ± 3.2 years for controls, with 73% being right handed and 33% being starting pitchers (Table 2). There were no differences in pitch counts or innings pitched in T1 between cases and controls (P = .30 and P = .10, respectively).

Table 2

Characteristics of Pitchers^a

	Case (n = 115)	Control (n = 230)	P Value
Age, y	27.9 ± 3.3	28.4 ± 3.2	.14
Height, cm	189.0 ± 6.0	188.9 ± 5.2	.98
Weight, kg	96.8 ± 7.6	98.2 ± 11.5	.18
Right-handedness, %	73.0	73.0	.98
Starting pitcher, %	33.0	33.0	.98
Draft position	274.6 ± 318.8	258.7 ± 270.2	.823
International free agent, %	15.0	25.0	.975
Innings pitched in T1	67.8 ± 57.1	57.5 ± 51.7	.10
Pitch count in T1	1064.9 ± 905.7	960.0 ± 847.4	.30

Data are shown as mean ± SD unless otherwise indicated. T1, season before injury.

In T1, large statistically significant differences in Pitching+ and Location+ for fastballs, changeups, and sinkers, and in Stuff+ for changeups, were identified (P < .05) (Table 3). Stuff+ did not significantly differ between cases and controls for all other pitches (P > .05).

Table 3

Preinjury Advanced Analytic Data in T1^a

	Stuff+			Location+			Pitching+
	Case	Control	P Value	Case	Control	P Value	Case	Control	P Value
Fastball	99.43 ± 21.70	95.20 ± 19.48	.28	100.80 ± 7.12	96.60 ± 14.02	.03	99.23 ± 9.28	93.61 ± 14.13	.01
Slider	108.07 ± 21.83	105.96 ± 16.51	.63	99.87 ± 7.26	98.23 ± 12.29	.39	106.10 ± 9.03	102.84 ± 11.75	.13
Changeup	95.08 ± 24.45	85.17 ± 22.10	.04	101.64 ± 12.63	93.81 ± 19.31	.01	100.78 ± 14.54	91.38 ± 19.93	.01
Curveball	103.41 ± 13.67	99.47 ± 21.62	.36	96.95 ± 8.95	98.64 ± 14.61	.56	103.73 ± 11.81	100.47 ± 10.94	.28
Cutter	94.50 ± 10.32	99.55 ± 13.78	.25	100.75 ± 9.59	95.15 ± 11.68	.15	97.83 ± 8.10	93.30 ± 10.89	.19
Sinker	98.44 ± 18.91	94.07 ± 16.81	.33	105.92 ± 14.07	95.74 ± 23.72	.02	104.08 ± 16.82	91.35 ± 22.76	.01

Data are shown as mean ± SD. Stuff+, Pitching+, and Location+ are all scaled similarly to intelligence quotient; a score of 100 is graded out as league average. Significant P values (ie, <.05) are indicated in boldface. Data for splitters were omitted because of an insufficient sample size. T1, season before injury.

Additionally, cases had a significantly superior velocity and less horizontal release point for fastballs, changeups, and sinkers, along with an increased HAA above average for fastballs and sinkers. There was also a significantly increased spin rate for sliders, an increased HAA for sinkers, and an increased release extension for cutters (P < .05) (Table 4).

Table 4

Preinjury Pitch-Tracking Data in T1^a

	Fastball	Slider	Changeup	Curveball	Cutter	Splitter	Sinker
Velocity, mph
Case	94.22 ± 2.71	84.91 ± 3.30	86.28 ± 3.19	78.91 ± 3.49	89.11 ± 2.85	85.20 ± 2.54	93.62 ± 2.93
Control	93.29 ± 2.32	84.12 ± 2.97	85.27 ± 2.86	78.66 ± 3.34	88.68 ± 2.65	85.97 ± 2.80	92.78 ± 2.52
Spin rate, rpm
Case	2282.00 ± 161.00	2423.00 ± 224.00	1775.04 ± 292.48	2452.62 ± 342.70	2297.80 ± 276.24	1445.76 ± 245.82	2204.79 ± 176.04
Control	2262.00 ± 134.00	2344.00 ± 212.00	1740.00 ± 265.00	2444.00 ± 239.00	2319.00 ± 179.00	1533.00 ± 305.00	2168.00 ± 157.00
Active spin
Case	0.90 ± 0.09	0.38 ± 0.13	0.93 ± 0.08	0.65 ± 0.21	0.57 ± 0.16	0.88 ± 0.02	0.88 ± 0.08
Control	0.90 ± 0.08	0.40 ± 0.14	0.92 ± 0.08	0.73 ± 0.14	0.45 ± 0.10	0.90 ± 0.08	0.88 ± 0.08
Spin axis, deg
Case	193.84 ± 34.20	162.92 ± 93.42	204.02 ± 61.17	116.47 ± 119.84	182.64 ± 24.83	210.72 ± 61.38	197.35 ± 41.81
Control	191.37 ± 36.32	162.97 ± 84.64	197.45 ± 52.60	103.50 ± 114.32	174.44 ± 29.52	207.85 ± 45.92	188.82 ± 46.60
Horizontal movement, inches
Case	7.57 ± 3.30	6.05 ± 3.86	13.10 ± 3.33	8.72 ± 3.68	3.29 ± 1.40	11.74 ± 1.94	14.59 ± 2.45
Control	7.77 ± 3.36	5.71 ± 3.84	12.93 ± 3.08	8.42 ± 3.77	3.19 ± 1.36	11.04 ± 3.98	14.33 ± 2.47
Vertical movement, inches
Case	15.83 ± 2.55	1.45 ± 4.01	7.69 ± 4.29	−8.77 ± 5.54	8.75 ± 2.96	5.42 ± 4.90	11.00 ± 4.30
Control	15.57 ± 2.87	1.89 ± 3.76	7.79 ± 4.24	−8.03 ± 5.81	8.01 ± 3.60	6.76 ± 4.58	9.88 ± 4.59
Horizontal release point, ft
Case	1.76 ± 0.73	1.96 ± 0.74	1.97 ± 0.72	1.74 ± 0.67	1.94 ± 0.63	1.63 ± 0.82	1.87 ± 0.75
Control	1.96 ± 0.73	2.07 ± 0.72	2.11 ± 0.71	1.98 ± 0.72	2.04 ± 0.75	1.68 ± 0.63	2.14 ± 0.73
Vertical release point, ft
Case	5.98 ± 0.46	5.88 ± 0.53	5.84 ± 0.49	6.05 ± 0.36	5.94 ± 0.35	6.08 ± 0.48	5.86 ± 0.53
Control	5.88 ± 0.55	5.80 ± 0.58	5.80 ± 0.50	5.98 ± 0.39	5.91 ± 0.50	6.01 ± 0.28	5.75 ± 0.65
HAA, deg
Case	−1.22 ± 0.93	−2.95 ± 1.38	−0.36 ± 0.97	−2.73 ± 1.09	−2.65 ± 0.57	−0.27 ± 0.86	–0.24 ± 0.83
Control	−1.37 ± 0.88	−3.15 ± 1.21	−0.51 ± 0.94	−2.99 ± 1.29	−2.91 ± 0.73	−0.32 ± 0.79	–0.50 ± 0.85
HAA above average
Case	0.45 ± 0.80	−0.92 ± 0.91	0.64 ± 0.84	−1.04 ± 0.83	−0.44 ± 0.74	0.96 ± 0.91	0.95 ± 0.83
Control	0.25 ± 0.76	−1.00 ± 0.88	0.50 ± 0.78	−1.26 ± 0.97	−0.66 ± 0.83	0.74 ± 0.70	0.63 ± 0.79
VAA, deg
Case	−4.99 ± 0.57	−7.88 ± 0.86	−7.20 ± 0.78	−9.70 ± 0.84	−6.54 ± 0.82	−7.92 ± 0.68	−5.84 ± 0.58
Control	−5.05 ± 0.59	−7.89 ± 0.90	−7.20 ± 0.69	−9.59 ± 1.05	−6.61 ± 0.88	−7.57 ± 0.82	−5.90 ± 0.82
VAA above average
Case	0.86 ± 0.45	−0.76 ± 0.67	0.02 ± 0.66	−2.53 ± 0.88	0.10 ± 0.55	−0.45 ± 0.66	0.62 ± 0.51
Control	0.91 ± 0.50	−0.67 ± 0.74	−0.01 ± 0.53	−2.41 ± 0.85	0.03 ± 0.54	−0.19 ± 0.61	0.60 ± 0.54
Release extension, ft
Case	6.27 ± 0.45	6.02 ± 0.48	6.31 ± 0.46	5.93 ± 0.50	6.25 ± 0.33	5.92 ± 0.42	6.20 ± 0.41
Control	6.20 ± 0.43	5.99 ± 0.47	6.21 ± 0.45	5.85 ± 0.50	6.06 ± 0.46	5.94 ± 0.45	6.15 ± 0.44

Data are shown as mean ± SD. Statistically significant differences are indicated in boldface. Horizontal metrics were normalized for right-handed pitchers, yielding negative values. HAA, horizontal approach angle; mph, miles per hour; rpm, revolutions per minute; T1, season before injury; VAA, vertical approach angle.

During the 3 seasons before the injury, there was a significant decrease in vertical release point for cutters, along with a significant increase in vertical release point and decrease in release extension for splitters, for cases compared with controls (P < .05) (see Appendix Table A1, available in the online version of this article). No other significant changes in analyzed metrics were identified in the 3 seasons preceding the injury.

Binary logistic regression was conducted for each pitch to identify associations with UCL surgery. Notably, higher velocity fastballs, sliders, and changeups were all associated with UCL surgery, along with sliders with a higher spin rate and cutters with a longer release extension (Table 5).

Table 5

Pitch-Specific Metrics Associated With UCL Injury^a

	Fastball	Slider	Changeup	Curveball	Cutter	Sinker
Velocity
Coefficient	0.15	0.11	0.10	0.04	0.02	0.08
95% CI	0.05 to 0.25	0.006 to 0.21	0.007 to 0.20	−0.06 to 0.13	−0.21 to 0.26	−0.04 to 0.19
P value	.004	.04	.04	.45	.89	.21
Spin rate
Coefficient	<0.001	0.002	<0.001	−0.0001	0.001	0.002
95% CI	−0.001 to 0.002	0.0004 to 0.003	−0.001 to 0.001	−0.001 to 0.001	−0.002 to 0.005	−0.0001 to 0.004
P value	.45	.01	.47	.78	.43	.08
Horizontal release point
Coefficient	−0.10	−0.27	−0.38	−1.03	1.58	−0.48
95% CI	−0.83 to 0.61	−1.14 to 0.57	−1.14 to 0.59	−2.08 to 0.04	−0.46 to 3.78	−0.69 to 1.67
P value	.78	.54	.44	.054	.14	.42
HAA above average
Coefficient	0.26	−0.10	−0.13	−0.44	1.94	0.94
95% CI	−0.42 to 0.94	−0.86 to 0.63	−1.00 to 0.76	−1.30 to 0.34	0.04 to 4.02	−0.12 to 2.05
P value	.45	.44	.77	.28	.052	.09
Release extension
Coefficient	0.38	0.22	0.40	−0.13	1.66	−0.40
95% CI	−0.16 to 0.92	−0.33 to 0.78	−0.19 to 1.00	−0.46 to 0.73	0.27 to 3.25	−0.27 to 1.10
P value	.17	.44	.19	.66	.03	.25

Binary logistic regression utilizing data from the season before surgery was conducted to determine pitch-specific metrics associated with an injury and to help eliminate confounding, given the large amount of variables included in our unpaired t tests. Multiple pitches could not be included in the same logistic regression analysis, given the differences in pitch arsenals among the included pitchers (eg, not every pitcher threw a slider, a curveball, etc) and to not dilute our analysis. Our judgment was used to exclude certain variables related to each other (eg, Pitching+ is heavily influenced by Stuff+ and Location+). Boldface P values indicate statistical significance (P < .05). HAA, horizontal approach angle; UCL, ulnar collateral ligament.

Discussion

This study investigated a number of pitch-specific advanced analytic and pitch-tracking metrics as potentially new variables to assess the UCL injury risk. Given the differences in each pitcher’s arsenal and pitching trends that favor certain pitches and movement profiles, pitch-specific data are critical to develop safer player development protocols and more targeted injury prevention initiatives.^5,7,22,24,44 This study demonstrated that pitch-specific associations with UCL surgery exist compared with matched controls. Specifically, higher velocity fastballs, sliders, and changeups were all associated with UCL surgery, along with sliders with a higher spin rate and cutters with a longer release extension. Fastballs, changeups, and sinkers with superior ability (Pitching+) and command (Location+) were also associated with UCL surgery. While fastball velocity appears to play a role in the rise of UCL injuries, recent trends in decreased fastball usage and improved secondary pitches suggest that an increased focus on entire pitching arsenals is warranted. Altogether, we hope that this study provides better insight for players and teams on pitch-specific factors that may put them at an increased risk for injuries.

Our secondary objective was to analyze whether large season-to-season changes in pitch-specific pitch-tracking metrics independently were associated with UCL surgery. The significant financial stakes of performing in MLB has put increased pressure on player development without fully understanding the potential risk of injuries with a rapid improvement in pitch arsenals. Weighted ball programs are frequently used to gain velocity, despite many pitchers attributing injuries to the regimen and some evidence of an increased injury risk.^12,36 Training facilities equipped with high-resolution cameras and biomechanical sensors that enable pitchers to experiment with different pitches, release points, grips, and more are now commonplace. Pitchers can more commonly make significant improvements in only one off-season, but the potential injury risk of this improvement and increased stress on a pitcher’s elbow are unknown. Reassuringly, no significant differences in changes in velocity, spin rate, movement, or approach angle for any pitch were observed. Pitchers who lowered the vertical release point of their cutters, and raised the vertical release point while reducing the release extension of their splitters, were associated with UCL surgery. The clinical significance of these data is unknown and would require further biomechanical analysis. Given the limited publicly available data on advanced analytics such as Stuff+, Location+, and Pitching+, which were developed in 2020, we were not able to analyze how season-to-season changes in these metrics impacted UCL surgery rates. Investigating these factors is likely the most effective way to determine whether making large improvements across multiple metrics is a risk factor for an injury, as these novel analytics capture the synergistic effect of multiple underlying physical metrics.

Recently, LaPrade et al²³ highlighted the importance of incorporating advanced sporting metrics into risk factor and return-to-play analyses. Most studies involving MLB pitchers have focused primarily on traditional descriptive statistics (such as wins, innings pitched, return to competition level) or rate-based performance statistics with inherent variability (such as earned run average or walks plus hits per inning pitched).^{11,21,27,35,37,38,40} Previous studies have also reported on velocity, pitch count, and pitch type/usage when evaluating the injury risk.^{2,3,5-7,11,16,22,35,39} Prodromo et al³⁵ found that increased velocity increased the risk of UCL injuries, while others found that increased fastball or curveball usage were risk factors for an injury or arm pain.^{2,3,5-7,11,16,22,39}

Although velocity is now a well-established risk factor for UCL injuries, our study suggests that specifically increased velocity of fastballs, sliders, sinkers, and changeups were associated with UCL surgery over the past 5 seasons. Pitchers have been throwing fastballs less in recent years,⁹ as teams realized that hitters have the most success with fastballs, leading to the increased use of sinkers or cutters, which in theory can be more difficult to hit because they have “late” movements but are still thrown at high velocities.^19,30 Reports have outlined the increased sinker velocity also seen throughout the league in recent years.^9,31 While the rate of fastballs thrown over 95 mph has nearly doubled in the past 15 years, the rate of sinkers being thrown over 95 mph has nearly quadrupled to 28%.³¹ Sinkers also have more total movement than any other pitch, as they showed in this study, and are popular in player development to maximize the effect of seam-shifted wake.¹⁹ In our study, cases had a higher mean sinker velocity than the mean fastball velocity of matched controls. In contrast, controls threw significantly more cutters, which are generally a slower alternative with less movement than fastballs or sinkers. While most studies have focused on fastball velocity, our previous study identified that decreased fastball usage was associated with UCL surgery.²⁶ In addition, we found that the increased velocity of off-speed pitches such as sliders and changeups were associated with UCL surgery. This suggests that increased focus should be placed on the velocity of all pitches, rather than only fastballs.

Changeups, which have a lower velocity, spin rate, and movement, were previously shown to have decreased torque on pitching shoulders and elbows.^13,15 Changeups were often regarded as “safe” pitches, and this is likely true, given the previously published biomechanical data and relatively modest pitch-tracking data that we have collected.^13,15 However, recent trends in how pitchers have been throwing their changeup with increased velocity, Stuff+, Location+, and Pitching+ may have made a previously “safe” pitch one that can meaningfully contribute to injury risk. Given that UCL injuries in pitchers are commonly caused by chronic overuse, any increase in stress from a pitch could be clinically meaningful over time. Further biomechanical analysis should investigate the load placed on elbows at modern velocities and movement profiles.

Increased velocity and overall command (Location+) seem to be driving the improvements in Stuff+ and Pitching+ of fastballs, sinkers, and changeups. The most effective pitchers in MLB tend to grade out high in Stuff+.¹⁴ Command is critical for success and is often what distinguishes the elite pitchers, but only our previous report has shown that improved command is associated with UCL surgery.²⁶ Increased physical and mental strain associated with improved accuracy could theoretically increase the risk of injuries, and given the relative lack of movement with changeups, command can be more important to achieve success. Command can also be influenced by pitch repetition and thus increased workload, possibly in practice sessions. Increasing spin rate has been a major goal for player development in recent years,^17,32 with increased spin leading to enhanced perceived velocity, differing ball trajectories, and worse hitting performance.^19,32 Mayo et al²⁷ examined changes in various pitch type spin rates that predisposed to UCL injuries in the prior 15 games. Sliders have previously been shown to be associated with elbow pain¹⁵ and, along with curveballs, have the highest spin rate of other pitches. Slider usage has increased throughout the league and has become one of the most popular pitches in the pitch-tracking era,³⁰ which can be attributed to a number of factors. Based on grip, a slider is released with the ball above the pitcher’s fingers and can be thrown at a higher velocity than a curveball, which is generally released with the player’s fingers on top of the ball. This makes it more difficult for hitters to recognize sliders while also having a shorter time to react from the increased velocity.³⁰ Our data suggest that these higher velocity and spin rate sliders are associated with UCL surgery. Sliders also have a wider variability in their movement profiles, with some pitchers even utilizing 2 different versions of a slider, with one having more vertical movement and another having more horizontal movement. Further research is warranted to better characterize the injury risk of sliders, especially now that MLB is characterizing “sweepers” as a new pitch, which was often previously characterized as a slider that primarily had horizontal movement until it was distinguished in 2023.

Some studies have shown that a sidearm delivery may predispose to UCL injuries.¹ Cohen et al¹⁰ found a more horizontal release point to be a risk factor for injuries, while Whiteside et al⁴⁴ found a more horizontal release point to be protective of injuries using PITCHf/x data, which was replaced by Trackman cameras in 2017. The clinical significance of horizontal release point is also unclear, as pitchers can vary their horizontal release point and approach angle simply by shifting their starting position on the mound. It is unknown how commonly pitchers alternate their stance on the mound, but HAA above average normalizes for these potential confounders and gives insight into the approach angle secondary to the pitcher’s mechanics.⁸ HAA above average findings indicated that pitchers throwing fastballs and sinkers with a horizontal break at sharper angles toward the pitcher’s glove side were more associated with UCL surgery in t tests but were no longer significant in regression analyses. Vertical release point and approach angle cannot be as easily altered but were not associated with UCL surgery for any pitch. The clinical significance of release extension is unknown and can be a surrogate of several factors including stride length, arm extension, and release point. Cutters with a longer release extension were associated with UCL surgery in our study, but further analysis is needed before any meaningful conclusions can be made. Biomechanical analyses are warranted to investigate whether certain kinematic changes in pitching delivery can be made to mitigate the injury risk.

Limitations

This study is not without limitations. While statistical significance for some metrics was obtained, the clinical significance of these findings is unknown. The results of individual t-tests should be interpreted with caution given the large number of variables included in this analysis, but our logistic regression accounted for testing multiple variables at once. Entirely public data was used for this study, although the majority of this data is released directly by MLB and these sources have been used multiple times previously.^{9,20,22,26,27,34,43} Obtaining official league injury data can be difficult, and improved collaboration between sports leagues and researchers is needed to best characterize the injury prevalence and improve prevention.²³ Increased workload is a known risk factor for UCL injuries and may have played a role in our study, despite the difference in innings pitched not being statistically significant (P = .10). It is possible that more dominant pitchers are pitching later and more efficiently in games, as the lack of difference (P = .30) in pitch count was well powered and confirms that cases and controls were matched appropriately to allow for other comparisons. Only pitches thrown in a live MLB game were counted in this analysis, excluding pitches thrown during practices, which can also likely affect the injury risk. Despite these limitations, this study represents a significant addition to our understanding of pitch-specific risk factors for a UCL injury in MLB pitchers, as called for by LaPrade et al.²³

Conclusion

This study investigated a number of pitch-specific advanced analytic and pitch-tracking metrics as potentially new variables to assess UCL injury risk and demonstrated that pitch-specific associations with UCL surgery exist compared to matched controls. Higher velocity fastballs, sliders, and changeups were all associated with UCL surgery, along with sliders with a higher spin rate and cutters with a longer release extension. Fastballs, changeups, and sinkers with superior ability (Pitching+) and command (Location+) were also associated with UCL surgery. While fastball velocity appears to play a role in the rise of UCL injuries, recent trends in decreased fastball usage and improved secondary pitches suggest that an increased focus on entire pitching arsenals is warranted. Altogether, we hope that this study provides better insight for players and teams on pitch-specific factors that may put them at an increased risk for injuries. Future collaboration with MLB to develop additional biomechanical data is warranted to more clearly identify risk factors for UCL injuries.

Supplemental Material

sj-png-1-ajs-10.1177_03635465251330564 – Supplemental material for Pitch-Specific Advanced Analytic and Pitch-Tracking Risk Factors for Ulnar Collateral Ligament Injuries in Major League Baseball Pitchers

Supplemental material, sj-png-1-ajs-10.1177_03635465251330564 for Pitch-Specific Advanced Analytic and Pitch-Tracking Risk Factors for Ulnar Collateral Ligament Injuries in Major League Baseball Pitchers by Michael A. Mastroianni, Jennifer A. Kunes, John D. Mueller, Kyle K. Obana, Jamie Confino, Andrew J. Luzzi, Alexander J. Rondon, David P. Trofa, Charles A. Popkin, Charles M. Jobin, William N. Levine and Christopher S. Ahmad in The American Journal of Sports Medicine

Footnotes

Acknowledgements

The authors acknowledge Eno Sarris of The Athletic and Max Bay as the developers of the statistics Stuff+, Location+, and Pitching+ referenced in this article. They also acknowledge Alex Chamberlain and Jon Roegele for their public data collection and insight into data analysis used in this study.

Submitted June 21, 2024; accepted February 11, 2025.

One or more of the authors has declared the following potential conflict of interest or source of funding: A.J.R. has received hospitality payments from Stryker and support for education from Paladin Technology and Liberty Surgical. D.P.T. has received hospitality payments from Gotham Surgical and Arthrex. C.M.J. has received consulting fees from Zimmer Biomet, Smith & Nephew, and Medical Device Business Services and speaking fees from DePuy Synthes and Acumed. W.N.L. has received consulting fees from Zimmer Biomet, DePuy Synthes, and Medical Device Business Services and royalties from Zimmer Biomet. C.S.A. has received consulting fees and royalties from Arthrex. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

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