Temperature and aggression revisited: Evidence from 1 million amateur football matches.

A large body of research documents a positive relationship between temperature and human aggression, underpinning projections of increased conflict in a warming climate. However, most prior evidence relies on laboratory experiments with convenience samples or on crime records, both of which are limited in their generalizability to everyday social interactions. To isolate the effect of temperature in a standardized, real-world social environment, we analyze ∼1 million amateur football matches played across Germany and study aggression among more than one million amateur players. Comparing matches played at the same venue within the same league and season, and adjusting for referee and team differences, we find a precisely estimated inverted-U relationship between temperature and player aggression: disciplinary cards (issued by referees for fouls and misconduct) increase with temperature up to ∼13 °C but decline thereafter. Matches played under extreme heat show a 15% reduction in disciplinary actions relative to the sample mean. Our results contribute to the temperature-aggression literature: in line with affect-based accounts of aggression, moderate warmth may increase irritability and arousal; however, to the extent that aggressive behavior requires physical engagement, it may decline at extreme temperatures.