We exploit the natural experimental setting provided by the Covid-19 lockdown to analyse how performance is affected by a friendly audience. Specifically, we use data on all football matches in the top-level competitions across France, Germany, Italy, Spain, and the United Kingdom over the 2019/2020 season. We compare the difference between the number of points gained by teams playing at home and teams competing away before the Covid-19 outbreak, when supporters could attend any match, with the same difference after the lockdown, when all matches took place behind closed doors. We find that the performance of the home team is halved when stadiums are empty. Further analyses indicate that offensive (defensive) actions taken by the home team are drastically reduced (increased) once games are played behind closed doors. The referee is affected too, as she changes her behaviour in games without spectators. Finally, the home advantage is entirely driven by teams that do not have international experience. Taken together, our findings corroborate the hypothesis that social pressure influences individual behaviour.