Effects of large gatherings on the COVID-19 epidemic: Evidence from professional and college sports

•We compare COVID-19 case loads and mortality across counties that hosted more versus fewer NHL hockey games, NBA basketball games, and NCAA basketball games in March of 2020, before any large outbreaks were identified.•We find that hosting one additional NHL/NBA game in March 2020 led to an additional 7520 cases and 658 deaths.•Similarly, we find that hosting an additional NCAA Division 1 men's basketball game in March 2020 resulted in an additional 34 deaths.•Back-of-the-envelope calculations suggest that the per-game fatality costs were 200–300 times greater than per-game spending. We compare COVID-19 case loads and mortality across counties that hosted more versus fewer NHL hockey games, NBA basketball games, and NCAA basketball games during the early months of 2020, before any large outbreaks were identified. We find that hosting one additional NHL/NBA game in March 2020 leads to an additional 7520 cases and 658 deaths. Similarly, we find that hosting an additional NCAA Division 1 men's basketball game in March 2020 results in an additional 34 deaths. Back-of-the-envelope calculations suggest that the per-game fatality costs were 200–300 times greater than per-game spending.