Abstract
Background:
In 2023, Major League Baseball (MLB) implemented a pitch clock (PC) to reduce game duration. Concerns have emerged regarding its effect on injury rates, particularly ulnar collateral ligament (UCL) tears, by reducing recovery time between pitches.
Purpose:
To assess the correlation between the MLB PC and UCL injury.
Study Design:
Cohort study; Level of evidence, 3.
Methods:
UCL tear incidence was compared between pre-PC (PPC) (2021-2022) and PC (2023-2024) eras. Data on UCL injuries were collected from publicly available databases. Variables collected included player demographics, advanced pitching metrics, total pitches, innings pitched, and games played. The primary outcome was UCL tear incidence per 1000 innings pitched. Secondary outcomes included UCL tears per innings pitched in the season of injury (preinjury workload innings [PIWi]) and UCL tears per pitches thrown in the season of injury (preinjury workload pitches [PIWp]), pitch count per season, fastball velocity, and pitch selection.
Results:
There was no significant difference in UCL tear incidence between PPC (0.63) and PC (0.67) eras (P = .73). However, PIWp was significantly higher in the PC era (n = 721) compared with the PPC era (n = 442) (P = .009), and PIWi was significantly higher in the PC (45.7) era compared with the PPC era (26.5) (P = .003). Pitchers in the PC group were significantly younger (28.4 vs 31.0) (P = .0002), threw more pitches per season (710 vs 441) (P = .02), and averaged more pitches per game (54.9 vs 35.5) (P = .0005).
Conclusion:
The PC had no observed effect on overall UCL tear incidence but was associated with a higher preinjury workload. These findings challenge fatigue-related injury theories and suggest potential protective effects of the PC.
At the start of the 2023 season, Major League Baseball (MLB) implemented a pitch clock (PC) beginning in spring training, which reduced the mean game duration by 20 to 30 minutes. While the PC has been praised for improving the pace of play, its potential effect on injuries has sparked controversy. Players and analysts have raised concerns that this change may inadvertently increase the rate of injuries, particularly ulnar collateral ligament (UCL) tears, by reducing the time available for recovery between pitches. 9 Some pitchers have gone so far as to accuse MLB of prioritizing game speed over player safety, intensifying the debate between MLB leadership and the MLB Players Association. 13 While the potential effect of the rule changes on injury rates has not been thoroughly examined, this gap in knowledge is particularly important given the high preexisting rate of UCL injuries among professional pitchers, which appeared to be increasing before the implementation of the PC.4,7
Injuries among pitchers have been on the rise for years, long before the implementation of the PC, reflecting the cumulative effects of evolving pitching trends, training regimens, and many other factors.3,6 This has raised concern among sports medicine physicians, prompting careful attention to pitching regulation in youth sports and beyond. 15 In this setting, the introduction of the PC represents a significant rule change that has undeniably altered several relevant facets of the game. By accelerating the tempo, it has affected recovery time between pitches, the pacing of the game, and even the mental preparation of pitchers, adding a new layer of complexity to an already demanding role.
Previous studies have identified key risk factors for UCL injury, including pitch velocity, pitch type, and cumulative workload. 5 Biomechanical studies have further elucidated these risk factors by demonstrating that increased torque at the elbow during high-velocity pitching significantly strains the UCL and correlates with player injury. 1 Further biomechanical analyses by Wang et al 20 and Anz et al 1 have described the critical roles of the flexor carpi ulnaris and flexor digitorum superficialis in stabilizing the elbow and reducing tension on the UCL by promoting a varus force. Intuitively, it follows that the UCL should be at higher risk, as it loses secondary support from the flexor carpi ulnaris and flexor digitorum superficialis with fatigue. However, current literature blurs this intuition. A study by Escamilla et al 8 found no correlation between the onset of muscular fatigue and altered biomechanics or increased forces on the elbow. 20
While many have speculated that the PC may increase UCL injuries, it is important to consider potential positive ramifications for pitchers. Schwartz 17 reported that mean fastball velocity across the league decreased by 0.3 mph with bases empty and 0.2 mph with runners on. This reduction in velocity may indicate a shift in emphasis from maximal exertion to a focus on pitcher longevity. A recent memorandum released by the MLB commissioner in December of 2024 explicitly attributed the rise in pitcher injuries to factors such as rising velocities, pitch selection, and the relentless drive for maximal effort. In this memorandum, reference was also made to the introduction of the PC. However, the commissioner also stated that there is insufficient evidence to link the increasing concern of UCL injuries to any of the aforementioned factors. 14
This study aims to address this gap by determining whether a correlation exists between the implementation of the MLB PC and a change in incidence of UCL injuries in professional pitchers. By providing critical insights into the relationship between pace-of-play modifications and pitcher health, this research seeks to inform MLB leadership, the MLB Players Association, and the broader sports medicine community about the implications of these rule changes.
Methods
This retrospective cohort study evaluates the effect of the PC on the incidence of UCL tears among MLB pitchers by comparing 2 time periods: the pre-PC (PPC) era (2021-2022) and the PC era (2023-2024). The study population included pitchers who sustained documented UCL tears and underwent surgical treatment during these periods. Inclusion criteria required players to be active MLB pitchers during the specified seasons. Position players, and pitchers listed as position players at the time of injury, were excluded from this study. The players who were diagnosed with UCL tear but did not go on to have surgery were not included in our data set due to lack of public record.
Data collection was performed using publicly accessible injury databases, including the MLB Player Analysis spreadsheet, which documents all known surgically repaired or reconstructed UCL tears in professional baseball, and advanced statistics from baseballsavant.mlb.com. The following variables were recorded for statistical analysis: player demographics (age, handedness, years of MLB experience), injury characteristics (date, treatment type), pitching metrics (mean velocity, mean pitch count per game, total innings pitched, mean pitches per inning, mean fastball velocity, and percentage of pitch type stratified by fastball, breaking ball, or changeup), games pitched before UCL tear (within the season of injury), and history of previous UCL injuries or Tommy John surgery.
The primary outcome was UCL injury incidence per 1000 innings pitched. UCL injury incidence was calculated as the number of injuries divided by the total innings pitched across each era. Total innings pitched were summed over the 2-year periods for the PPC (2021-2022) and PC (2023-2024) eras, based on publicly available MLB season totals from baseball-reference.com. Secondary outcomes included mean total pitches thrown per season, mean innings pitched per season, mean fastball velocity, and the proportion of fastballs, breaking balls, and off-speed pitches per game. Preinjury workload was calculated as the number of pitches (PIWp) and innings (PIWi) before injury in the season in which the injury occurred.
As this study utilized publicly available data, individual player consent was not required, and all analyses complied with institutional guidelines for ethical data use.
Statistical Analysis
A power analysis determined the necessary sample size for detecting a significant difference in UCL tear incidence between the 2 groups. Assuming a Cohen d effect size of 0.3, an alpha level of .05, and 90% power, a minimum of 44 participants per group was required. Descriptive statistics were calculated using the Pandas Python library to summarize demographic and baseline characteristics, with means and standard deviations for continuous variables and frequencies and percentages for categorical variables. 11 Comparative analyses included t tests for comparing continuous variables and chi-square tests for categorical variables. A multivariate analysis was performed to determine if any variables significantly affected UCL injuries.
Results
The demographics and statistics comparing injured pitchers before and after the introduction of the PC revealed several key demographic differences (Table 1). There was a significant difference in the mean age of injured pitchers PPC at 31.0 years (range, 25-41) compared with 28.4 years (range, 21-37) PC (P = .0002). Number of seasons played in MLB before time of injury demonstrated no significant difference, with a mean of 4.437 seasons (range, 1.0-11) PPC compared with 4.44 seasons (range, 1-14) in the PC era (P > .05). After the introduction of the PC, there was a significantly higher total pitch count per season, in the season of injury, with 710 pitches in the PC group compared with 442 in the PPC group (P = .02), a 61% increase (Table 1, Figure 1). Pitch count per game was 54.9 PC compared with 35.5 PPC (P = .0005). Additionally, there was a significantly higher proportion of PPC starting pitchers with UCL injury, at 38.9% compared with 63.8% of PC starters (P = .007) (Table 2).
Demographics and Advanced Metrics for Both Groups a
Data are presented as mean ± SD. Bold P values indicate significant difference. PC, pitch clock; PPC, prepitch clock.
In the season of injury.
Entire career.
Total number of pitches thrown during the season of injury on the x-axis, with the y-axis showing the number of ulnar collateral ligament (UCL) tears in each group.
Starters Versus Relievers a
Bold P values indicate significant differences. PC, pitch clock; PPC, prepitch clock; RP, relief pitcher; SP, starting pitcher.
The mean fastball velocity was not significantly different between PC (94.0 ± 2.5 mph) and PPC (93.8 ± 2.3 mph) (P = .59), and no significant difference in pitch selection after the PC was noted (P > .05) (Figure 2). Multivariate logistic regression demonstrated that younger age (P = .008) and higher mean pitch count (P = .03) were independently associated with UCL injuries sustained during the 2023-2024 MLB season compared with the 2021-2022 season. Starter versus reliever status (P = .37), mean fastball velocity, fastball usage, pitches per inning, and number of games pitched were not significantly associated with the season of injury after adjustment for covariates (Figure 3).
A comparison between pitch selection of both groups. Pitches were stratified into the categories “fastball”, “breaking ball,” and “off speed.” Diamonds represent extreme outliers within data set.
Forest plot showing adjusted odds ratios (ORs) and 95% CIs from a multivariate logistic regression assessing predictors of ulnar collateral ligament injury during the 2023-2024 Major League Baseball season compared with the 2021-2022 season. An OR >1 indicated increased odds of injury in the 2023-2024 season, while an OR <1 indicated increased odds of injury in the 2021-2022 season. The dashed line represents the null value (OR, 1.0), indicating no difference in odds between seasons. FB, fastball.
During the PC period (2023-2024), there were 58 total injuries, with an incidence rate of 0.673 injuries per 1000 innings. In comparison, the PPC period (2021-2022) recorded 54 injuries, corresponding to an incidence rate of 0.630 injuries per 1000 innings. This difference in incidence rates was not statistically significant (P = .73). However, the PC group was able to perform significantly higher workloads before injury (PIWi and PIWp) (Table 3). After the introduction of the PC, significantly more pitches were thrown before injury (P = .009) and pitchers were able to complete more innings before injury (P = .003).
Injury Incidence and Preinjury Workload for Both Pitches and Innings a
Bold P values indicate significant difference. Overall injury incidence was not significantly different. PC, pitch clock; PIWi, preinjury innings workload; PIWp, preinjury pitches workload; PPC, prepitch clock.
Discussion
The relationship between the throwing motion and UCL injury is a complex issue with many contributing factors. It is well known that the throwing motion places undue stress on the medial elbow, predisposing throwing athletes to UCL injury, which is especially prevalent among baseball pitchers. Previous literature has described the flexor carpi ulnaris and flexor carpi radialis as playing a role in stabilizing the elbow during this valgus stress by placing a counteracting varus stress on the elbow, although how much of a role this plays in preventing injury remains unknown.1,8,20 We do know that elements such as velocity, spin rate, and cumulative workload have previously been described to affect the risk of UCL tear in pitchers, 5 although the effect of a PC on UCL injuries has not previously been explored.
Findings by Sonne and Keir 18 have previously shown that as fatigue becomes more prevalent, lack of muscular support acts as a mechanism for an increased risk of UCL tear. While it would stand to reason that a PC will reduce recovery time between pitches and encourage muscle fatigue, our study shows the PC to have no observed effect on UCL injury.
The PIWi and PIWp were both significantly higher in the PC group (P = .003 and P = .009), suggesting a potential protective benefit associated with the PC. This may suggest the threshold for number of innings and pitches thrown before injury occurs is much later with the implementation of the PC.
Although it is common in the literature to suggest fatigue can increase the load on the UCL and contribute to injury risk, this is contradicted by Escamilla et al, 8 where no correlation was found between the onset of muscular fatigue and altered biomechanics or increased forces on the elbow. 20 We propose this change could be attributed to the decreased amount of time pitchers spend on the bench between innings in the PC era compared with the PPC era. In the first year of the implementation of the PC, ESPN reported the number of 3.5-hour games in 2023 was 9 compared with 390 in the year 2021. The overall mean game time decreased by 30 minutes. 16 This may lead to fewer opportunities for pitchers to get cold before going back out to the mound. It is possible that with decreased downtime between innings, pitchers’ arms are staying warm, allowing them to increase the number of pitches thrown before injury.
Interestingly, fastball velocity did not significantly differ between groups. However, PC pitchers threw more pitches per game and logged more innings per season (P = .02 and P = .01, respectively). Notably, in this study, PC pitchers were able to pitch longer before sustaining injuries. This resulted in an incidence rate of 21.9 injuries per 1000 innings in the PC group compared with 37.8 injuries per 1000 innings in the PPC group, a statistically significant finding (P = .009). Our results challenge existing theories that link fatigue-related injury mechanisms to increased workload. These findings highlight a potential unintended benefit of the PC, which, while designed to improve the pace of play, may reduce UCL injury risk in MLB pitchers.
DeFroda et al 5 found a significantly larger number of UCL tears occurred in the first 3 months of the season. They also noted relief pitchers predominated those who were injured. Our study demonstrated potential increased longevity in the PC era given the significant increase in number of innings pitched and pitches thrown before injury. In our study, we also noted a significant decrease in the number of relievers who sustained UCL tears and an increase in the number of starters who sustained injuries in the PC era compared with the PPC era. More focused studies would need to be performed to determine if this is a new trend related to the implementation of the PC.
Our study also looked at other factors such as age. We found that, on average, players who tore their UCL in the PC group were 2.5 years younger (P = .0002). This finding is particularly concerning given the significant impact UCL injuries can have on a player's career, often requiring surgical intervention and a prolonged rehabilitation, potentially leading to diminished performance or an inability to return to previous levels of competition. 19
Limitations
Despite these compelling findings, this study has limitations. Limitations include the retrospective design and reliance on publicly available injury data. The accuracy of our findings may be limited by the heterogeneity of publicly obtained data, which have been called into question in the sports medicine literature. 19 Additionally, unmeasured confounders, including variations in training regimens, recovery practices, or foreign substance use, may have influenced the results. For example, a study by Barrack et al 2 identified several modifiable physical characteristics, such as lumbopelvic stability, internal rotation strength, and scaption strength that coaches and clinicians can address to reduce torque on the elbow and potentially mitigate injury risk. The study by Melugin et al 12 emphasized the importance of stretching and focused strength training on injury prevention. Additionally, the amount of data available is limited because of the recent implementation of the PC. This topic would benefit from a larger data set to further examine the effects of a PC on pitcher injuries.
While this research sheds light on potential implications of the PC, further prospective and biomechanical studies are necessary to confirm causation and explore targeted injury prevention strategies. Moving forward, MLB leadership, the MLB Players Association, and sports medicine professionals must collaborate to optimize recovery protocols, refine training regimens, and reassess pitching schedules to ensure the sustainability of modern baseball. Prioritizing evidence-based approaches will be key to safeguarding pitcher health while maintaining the integrity and appeal of the sport.
Conclusion
This study found no significant difference in the rate of UCL tears per mean player exposure among MLB pitchers since the institution of the PC. However, it was noted that pitchers are throwing substantially more innings on average before injury in the PC era. Additionally, we found that injured pitchers were on average throwing 61% more pitches per season before injury in the PC era. Previous literature has documented increased workload as a risk factor for UCL injury. However, our findings suggest a year-over-year change in the relationship between pitcher workload and injury. Implementation of the PC may be protective for players, increasing the workload threshold for UCL injury.
Footnotes
Final revision submitted May 7, 2025; accepted May 20, 2025.
The authors declared that there are no conflicts of interest in the authorship and publication of this contribution. 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.
Ethical approval was not sought for the present study.
