The COVID-19 pandemic has decelerated substantial parts of economic and human interaction. This paper estimates football matches’ contribution to the spread of COVID-19 during Germany’s second infection wave in summer and autumn 2020. Exploiting the exogenous fixture schedules of matches across German counties in an event study design, we estimate that one additional match in a county on average raises daily cases by between 0.34 to 0.71 cases per 100,000 inhabitants after three weeks. Hence, this implies an increase of the seven-day incidence per 100,000 inhabitants by around three to seven percent. We do not find qualitatively different results for a subsample of German top league matches with the strictest hygiene regulations or matches with higher occupancy levels. Notably, the found effect is mediated by the incidence level at the day of the match with very few infections for matches at a seven-day incidence below 25. Using mobile phone data, we identify strong increases in the local mobility as an underlying mechanism. We finally show that the ban of away fans successfully limited the spread of COVID-19 beyond county borders. Our results alert that even outdoor mass gatherings can remarkably cause infections.