Do baseball pitchers hit batters more often when it’s hot outside?
Archival data from major league baseball games played during the 1986, 1987, and 1988 seasons (total N = 826 games) were used to assess the association between the temperatures at the games and the number of batters hit by a pitch during them. A positive and significant relationship was found between temperature and the number of hit batters per game, even when potentially confounding variables having nothing to do with aggression were partialed out. A similar relationship was found for games played during the 1962 season. The shape of this relationship appears to be linear, suggesting that higher temperatures lead major league pitchers to become more aggressive in pitching to batters.
Source: “Temper and Temperature on the Diamond: The Heat-Aggression Relationship in Major League Baseball” from Personality and Social Psychology Bulletin
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