Abstract
Background:
Major League Baseball (MLB) implemented a new foreign substance policy in June 2021. The effect of the new policy on pitcher injuries, wild pitches, hit batters, and pitching statistics is unknown.
Purpose:
To determine the effect of the new foreign substance policy regarding grip enhancement before and after its implementation on pitcher injury rate, wild pitches, hit batters, base on balls, strikeouts (SO), and home runs (HR).
Study Design:
Descriptive epidemiology study.
Methods:
MLB pitchers from the 2019 season were retrospectively compared with the pitchers from the 2022 season. Data were retrospectively collected on injuries and pitching statistics utilizing publicly available data. Primary outcome measures included pitcher injury rate, wild pitches, and hit batters. Secondary outcome measures included base on balls, SO, and HR. A nonparametric Wilcoxon rank-sum test was utilized for computing P values when comparing unadjusted non-normally distributed continuous outcomes and covariates between 2019 and 2022, which was adjusted for number of batters faced using either a linear regression model for adjusting means or a quantile regression model for adjusting medians.
Results:
In total, 828 pitchers in the 2019 season and 867 pitchers in the 2022 season were evaluated and included in this analysis. Pitcher overall injury rate per 1000 batters faced, hit batters, and SO did not show a statistical difference (P > .05). There was a statistically significant decrease in the adjusted number of wild pitches (2.9 vs 2.51; P = .04), adjusted earned run average (ERA) (4.51 vs 3.75; P < .01), adjusted base on balls (22.6 vs 21.1; P = .04), and adjusted HR (8.1 vs 6.1; P < .01) between the 2019 and 2022 seasons (P < .05).
Conclusion:
Our study showed that the effect of MLB policy enforcement regarding grip enhancement did not demonstrate a change in pitcher injury rate, hit batters, or SO; however, there was a significant decrease in wild pitches, ERA, and base on balls. As a result, the new policy appears to maintain previous injury rate and pitching statistics while attempting to control for foreign substance use.
Baseball is considered America's pastime and provides the foundation for other American sports. This is highlighted by new revenue records set by Major League Baseball (MLB) in 2022, approaching $11 billion. 1 The increase in revenue has also resulted in an increase in salary for MLB players. MLB pitchers represent a large portion of a team's roster, and overall total pitcher financial investments approached $1.6 billion in 2014. 8 Given increases in guaranteed pitcher contracts, injuries have resulted in millions of dollars paid to pitchers who were unable to play.4,8,11 As a result, there is a financial incentive for MLB, teams, and players to minimize injuries while maximizing pitcher productivity.
In June 2021, MLB created a new policy regarding use and enforcement of foreign substances by pitchers. Before this, there was a fairly ubiquitous use of foreign substances by pitchers for grip enhancement, which lacked standardized enforcement policies. Commissioner Rob Manfred said in a statement, “I understand there's a history of foreign substances being used on the ball, but what we are seeing today is objectively far different, with much tackier substances being used more frequently than ever before. It has become clear that the use of foreign substance has generally morphed from trying to get a better grip on the ball into something else – an unfair competitive advantage that is creating a lack of action and an uneven playing field.” 2 As a result, the goal of the new policy was to level the playing field and create a standardized process for rule enforcement for the timing, frequency, and judgment of foreign substance use. The penalty for violating rules includes sanctions and up to a 10-game suspension. 2
Counterarguments offered by some pitchers include concerns for potential increased pitcher injury rate and increased injuries from wild pitches/hit batters secondary to less grip on the ball. Several factors have been identified in contributing to and preventing injuries related to pitching, which include number of pitches, innings pitched, pitch type, pitching mechanics, throwing program, and core and lower extremity conditioning programs.3-7,9,12 We do not know of any studies that address the effect of the new 2021 MLB foreign substance policy and enforcement on incidence of MLB pitcher injury rate and pitching statistics. The purpose of our study was to quantify the effect of MLB's implementation of the new policy and enforcement of foreign substances on incidence of pitcher injury rate, wild pitches, and hit batters. Secondary outcome measures include the effect on earned run average (ERA), base on balls (BB), strikeouts (SO), and home runs (HR). We hypothesized that the new foreign policy would not affect pitcher injury rate or pitching statistics.
Methods
Patient Population
Following institutional review board (IRB) evaluation, the study was determined to be an IRB-exempt study. We identified MLB pitchers in the 2019 season and 2022 season to evaluate the effect of the MLB new policy and enforcement regarding foreign substances. We selected the 2019 and 2022 seasons because they were the first complete seasons without and with the new policy, respectively. We avoided utilizing the 2020 season based on the assumption that COVID-19 was a significant confounding variable. Pitchers in the MLB were included if they had pitched ≥1 game, where “game” was defined as throwing a single pitch. Pitchers were excluded from the study if they had an injury that precluded them from pitching at all during the season.
Data Collection
Pitchers, pitching demographics, and pitching statistics including age, number of batters faced, innings pitched, hit batters, wild pitches, ERA, BB, SO, and HR were obtained from publicly available data (prosportstransactions.com). Pitchers that played for multiple teams had their records consolidated into a single record. As a result, the unit of analysis for a given year was at the individual pitcher level. Pitcher injuries and injury subcategories were obtained from publicly available data (baseball-reference.com) based on movement onto the injured list (IL). Injuries that were extending from a previous IL designation were only counted as a single injury.
Statistical Analysis
A nonparametric Wilcoxon rank-sum test was utilized for computing P values when comparing unadjusted non-normally distributed continuous outcomes and covariates between 2019 and 2022. The mean or median hit by pitch, wild pitch, and ERA outcomes were also compared between the 2 years adjusting for number of batters faced. The adjustment was carried out using either a linear regression model for adjusting means or a quantile regression model for adjusting medians (ERA, BB, SO, HR). The association between any of these continuous outcomes and the number of batters faced in each year was allowed to be nonlinear using restricted cubic splines. Overall injury rate and subcategorical injury rates were normalized to every 1000 batters faced, and P values for their comparison were computed using a Poisson test for comparing rates. Statistical significance was set at P < .05. Computations were carried out using R 4.3.0 (R Foundation for Statistical Computing).
Results
A total of 1695 pitchers were identified, 828 pitchers from the 2019 season and 867 pitchers from 2022 season (P = .23). Pitchers during the 2019 season were significantly younger than pitchers from the 2022 season (27.9 ± 3.6 years vs 28.6 ± 3.3 years; P < .01). Pitchers in 2019 compared with pitchers in 2022 faced a greater total number of batters (211,107 vs 200,442; P = .01) and batters per pitcher (255 vs 231; P = .01) (Table 1). There was a near perfect correlation (r = 0.998) (Figure 1) between number of innings pitched and number of batters faced; therefore, controlling for the number of batters faced also controls for the number of innings pitched and is not a separate covariate. As a result, we adjusted injury rates and other statistics to control for number of batters faced.
Pitcher Demographics a
Data are presented as mean ± SD or n (bold represents statistical significance). Pitching demographics comparing pitchers from the 2019 season to pitchers from the 2022 season. Both seasons had a similar number of pitchers. The pitchers in 2019 were significantly younger and faced additional batters compared with pitchers in 2022.
Number of batters faced (n = 1845 pitcher-years) has an almost perfect correlation (r = 0.998) with the number of innings pitched. Therefore, controlling for the number of batters faced also controls for the number of innings pitched. It is not a separate covariate.
Table 2 and Figure 2 detail the pitcher overall and subcategorical injury rates for pitchers in the 2019 season compared with the 2022 season. The total number of pitchers with ≥1 injury in the 2019 season was n = 336 pitchers (or 40.6%) compared with the 2022 season of n = 381 pitchers (or 43.9%). Injury rate was normalized to account for number of batters faced. The adjusted overall injury rate for pitchers per 1000 batters faced did not significantly differ between the 2019 and 2022 seasons (2.15 vs 2.40; P = .09). Furthermore, pitcher subcategorical injury rates, which included shoulder girdle, elbow/arm, forearm, hand, spine, hip, knee/thigh, leg, foot and ankle, core, and generalized soreness, were not statistically significant between the 2 seasons (P > .05).
Pitcher Injury Rate per 1000 Batters Faced a
Adjusted pitcher total and subcategorical injury rates per 1000 batters faced sustained during the 2019 and 2022 Major League Baseball seasons. No significant difference in overall or subcategorical injury rates was observed in pitchers between the 2 seasons.
Pitcher total and subcategorical injuries sustained during the 2019 and 2022 Major League Baseball seasons. No significant difference in overall or subcategorical injuries occurred between the 2 seasons.
Table 3 and Figure 3, A and B highlight the differences observed in primary and secondary outcomes between the 2019 season and 2022 season adjusted for batters faced. The primary outcome of hit batters did not significantly differ between the 2 seasons (2.8 ± 0.143 vs 2.90 ± 0.143; P = .64). Conversely, when comparing the 2019 season to the 2022 season there was a significant decrease in pitchers’ ERA (4.51 ± 0.139 vs 3.75 ± 0.134; P < .01) and wild pitches (2.90 ± 0.136 vs 2.51 ± 0.136; P = .04). The secondary outcome of SO did not show a significant difference between the 2019 and 2022 seasons (54.3 ± 1.09 vs 55.5 ± 1.04; P = .41). There was a statistically significant decrease in base on balls (22.6 ± 0.56 vs 21.1 ± 0.52; P = .04) and HR (8.1 ± 0.23 vs 6.1 ± 0.26; P < .01) from the 2019 season to the 2022 season.
Primary and Secondary Outcomes Adjusted for Number of Batters Faced a
Data are presented as mean ± SD (bold represents statistical significance). Adjusted primary and secondary outcome pitching statistics adjusted for number of batters faced.
Scatterplots that illustrate the regression models for (A) wild pitches and (B) hit by pitch controlling for batters faced.
Discussion
The major finding of our study demonstrated that there was no statistically significant difference in MLB pitcher injury rate per batter faced when comparing the 2019 to 2022 seasons (2.15 vs 2.40; P = .09). Foreign substance use by pitchers in the MLB has occurred since the inception of the sport. Previous policies were often subjective and difficult to enforce in a standardized manner. The goal of the MLB's new 2021 policy on foreign substances was to level the playing field and create a standardized process for rule enforcement. Counterarguments to the policy change highlight the theoretically increased injury risk to pitchers and batters with less grip on the ball. The results from our study suggest that the new policy appears to maintain previous injury rates and pitching statistics while attempting to control for foreign substance use.
It is important to control for covariates when comparing pitchers between seasons that may influence the overall results. There were a similar number of pitchers evaluated in the 2019 season compared with the 2022 season. In our cohort, pitchers in the 2019 season were significantly younger compared with pitchers in the 2022 season. The simplest explanation for this would be that pitchers in 2019 that remained in the league for the 2022 season were now older and this contributed to the difference. There is also the possibility that the rookie pitchers for 2022 were older compared with rookies in 2019. Given how close together the averages were, we believe the former hypothesis is more likely to account for the age difference. Additionally, pitchers in 2019 faced more batters overall and batters faced per pitcher compared with pitchers in 2022. The precise reason for this is unclear, but likely multifactorial in a way that would be difficult to quantify. Regardless, this statistically significant difference in batters faced represented a confounding variable that may introduce bias into our results. We controlled for this by adjusting the injury rate and pitching statistics to normalize for the number of batters faced when comparing between the 2019 and 2022 seasons.
Posner et al 10 highlight the epidemiology of injuries in MLB between 2002 and 2008. These authors found that pitchers had an overall injury rate of 4.19 per 1000 athlete-exposures per month, which was 34% higher compared with fielders. Furthermore, pitchers had an increased risk of upper extremity injuries and decreased risk of lower extremity injuries compared with other positions. 10 Similarly, our study found a similar incidence of pitcher injury rate and subcategorical injury analysis. This study did not show a statistically significant difference of pitcher injury rate per 1000 batters or in subcategorical analysis between the 2019 season and the 2022 season. The new 2021 MLB policy on foreign substances does not appear to have had a significant effect on the incidence of pitcher injury rate when normalized to batters faced.
Pitching statistics are a complex measure of pitching performance with a myriad of factors contributing to the end result. While it is challenging to attribute a single policy change to a change in performance across hundreds of pitchers, it is still important to try to quantify the change in statistics over time. As hypothesized, the study did not show a statistically significant difference in SO or hit batters when normalized to batters faced. However, in contrary to our proposed hypothesis, our study demonstrated a significant decrease in ERA, wild pitches, base on balls, and HR when normalized to batters faced. It would be counterintuitive and a premature assumption to conclude that the new policy improved pitching performance; however, a reasonable deduction would be that the new 2021 MLB policy change regarding foreign substances did not significantly negatively affect pitching performance or statistics.
Limitations
While this study is the first to address the grip enhancement policy change as it relates to MLB pitcher injury rate and performance, it is not without limitation. First, the study is retrospective in design, which introduces bias and limited data on the athletes. Second, a public database for statistics and injuries may not be as complete as the individual team statistics and injury reports. Furthermore, we categorized injuries based on movement onto the IL and therefore would have missed some injuries that did not require IL designation. Conversely, we believe that the publicly produced data are a good representation of the injury patterns and statistics from both seasons, as the sources would have had similar flaws at both time points. Third, we used number of batters faced to help normalize the data between the 2 seasons. However, this may have introduced statistical error, which would have been better controlled by looking at total number and types of pitches thrown. This number would be more specific and a covariate, but the data were unavailable. We believe that similar to innings pitched, batters faced would likely have a high correlation with the number of pitches thrown. This study is isolated to comparing 1 season on each side of the rule enforcement, which is a relatively short time table. As we accrue more data, it will be important to look at more seasons on either side of the policy change to evaluate true changes in number of injuries and statistics. Last, a confounding variable associated with our results is the inability to account for the effectiveness in controlling for use of foreign substances by pitchers. Despite these limitations, to our knowledge, this is the first attempt at quantifying the effects of the new MLB policy regarding pitcher injury rates and statistics.
Conclusion
Our study showed that the effect of MLB policy enforcement regarding grip enhancement did not demonstrate a change in pitcher injury rate, hit batters, or SO; however, there was a significant decrease in wild pitches, ERA, and BB. As a result, the new policy appears to maintain previous injury rate and pitching statistics while attempting to control for foreign substance use. This study serves as a baseline to further evaluate how grip enhancement policies affect pitcher injury rate and statistics.
Footnotes
Final revision submitted December 29, 2024; accepted January 6, 2025.
One or more of the authors has declared the following potential conflict of interest or source of funding: S.A.S. has received hospitality payments from Arthrex; education payments from Smith & Nephew, Arthrex, and Saxum Surgical; and a grant from Arthrex. N.E. is the head team physician for the LA Dodgers and a board member of the AAOS; receives publishing royalties from Wolter Kluwer; and has received royalties and speaking fees from Arthrex, and education payments from Micromed. S.K. has received hospitality payments from Arthrex and Stryker; education payments from Micromed, Prodigy Surgical Distribution, Saxum Surgical, and Smith & Nephew; and a grant from Arthrex and Medical Device Business Services. M.B. is a team physician for the LA Dodgers; is a board member of the AAOS; is a paid consultant for Arthrex, Vericel, and Smith & Nephew; receives IP royalties from Stryker; education payments from Arthrex, Micromed, and Saxum Surgical; hospitality payments from Stryker; and honoraria from Vericel. 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 for this study was obtained from Cedar-Sinai IRB (STUDY00002452).