It's not easy traveling to play 81 games a year across multiple time zones and the major league baseball schedule, 162 games, is the most grueling in professional sports.
Two papers outline how sleep and fatigue are key issues in performance, which makes sense. Fatigue may impair strike-zone judgment during the 162 game Major League Baseball season and a player's sleepiness can predict his longevity in the league, the authors conclude.
One study found that MLB players' strike-zone judgment was worse in September than in April in 24 of 30 teams. When averaged across all teams, strike-zone judgment was significantly worse in September compared with April. The statistical model demonstrated strong predictive value through the season.