This is a great summary of a solid study (in my opinion) that shows the effects of indoor sports events and the spread/impact of covid:
voxeu.org
Mass gatherings contributed to early COVID-19 mortality: Evidence from US sports
Social distancing is important to slow the community spread of COVID-19. This column studies the banning of mass gatherings, a comparably low-cost intervention. Exploiting exogenous variation in top-flight basketball and ice hockey games in the US, which arise due to the leagues' predetermined...
