Opposite effects of Covid-19 infection on pitchers and batters: a retrospective study on Chinese Professional Baseball League players.

Background: The influence of COVID-19 infection on elite athletes remains largely unknown, especially on baseball players. The goal of this study is to examine the actual performance of infected elite baseball players from the Chinese Professional Baseball League (CPBL) from a sabermetric point of view.
Methods: This was a retrospective observational cohort study. CPBL players who were infected with COVID-19 from April 27 ^th to May 31 ^st , 2022, were eligible for this study. The performance of study participants before and after COVID-19 infection was compared, and statistics from the batters and pitchers were analyzed separately.
Results: During the study interval, 56 players were infected with COVID-19, including 35 batters and 21 pitchers. After excluding injured players and players with inadequate playing opportunities, 23 batters and 12 pitchers were enrolled. For batters, there were no significant differences before and after COVID-19 infection. However, batters older than 28 years of age showed a decline in slugging percentage (0.372 vs. 0.292, P=0.049). Analysis of pitchers revealed significantly boosted fastball velocity after COVID-19 infection (142.10 km/h vs. 142.82 km/h, P=0.028) and improved strikeouts per nine innings (6.89 vs. 8.56, P=0.021).
Conclusions: COVID-19 might have a potential influence on professional baseball players. For batters, veteran players more than 28 years of age were more likely to be negatively affected by COVID-19, whereas the effect of COVID-19 on pitchers was generally positive, with significantly improved fastball velocity and K/9 numbers.