We use ghost matches induced by Covid19 in the Bundesliga, Germany’s top two football (soccer) divisions, to investigate whether audiences affect referees. We find that pre-Covid19 referees gave fewer fouls and yellow cards for the home team relative to the away team. These differences in fouls and cards changed during the ghost matches so that home teams were treated less favorably than before. This effect is concentrated in matches where support for the away team is particularly weak. The results provide evidence for a home bias in referee decisions through social pressure.