Declining Plate Discipline during the Major League Baseball Season May Be the Result of Fatigue (P01.260)

OBJECTIVE: We hypothesize that Major League Baseball players will experience increasing lapses in vigilance as the season progresses, resulting in worsening plate discipline. BACKGROUND: Frequent long-distance travel and few off days over several months predispose to fatigue in Major League Baseball. To test our hypothesis, we examined the number of times a batter chose to swing at a pitch outside of the strike zone (a ball), captured by the O-swing% statistic. This statistic, analogous to plate discipline, was chosen because it represents a negative outcome (i.e. swinging at a ball is always a mistake). DESIGN/METHODS: Using a searchable database (Fangraphs Inc; fangraphs.com), we tracked the frequency of Major League Baseball batters swinging at pitches outside of the strike zone. Records from 2006 to 2011 were compared to those from 2002 to 2005, as stimulant drugs were officially banned and formal testing enacted after 2005. Data were expressed in team-months as the percentage of pitches swung at outside of the strike zone to total number of pitches seen outside the strike zone (O-Swing%). RESULTS: A total of 30 teams were analyzed. There was a linear increase of O-Swing% over time (p CONCLUSIONS: Performance in strike-zone judgment consistently worsened through the season, and the effect increased following a ban on stimulants in 2005. This trend occurred despite potential gains from practice and repetition through the season. The increase in O-Swing% through the year suggests worsening vigilance and judgement, and may represent fatigue effect. Future research related to performance and fatigue appears warranted in Major League Baseball players and those engaged in other professional sports. Disclosure: Dr. Kutscher has nothing to disclose. Dr. Song has nothing to disclose. Dr. Wang has nothing to disclose. Dr. Upender has nothing to disclose. Dr. Malow has nothing to disclose.