The home advantage (HA) is a robust phenomenon in football whereby the home team wins more games and scores more goals than the away team. One explanation is that the home crowd spurs on home team performance and causes the referee to unconsciously favour the home team. The Covid-19 (COVID) pandemic provided a unique opportunity to assess this explanation for HA, as European football leagues played part of the 2019/2020 season with crowds present and concluded with crowds absent. Using multi-level modelling we compared team performance and referee decisions pre-COVID (crowd present) and during-COVID (crowd absent) across 4844 games from 15 leagues in 11 countries. HA (goals scored and points gained) was significantly reduced during-COVID, which reflected the inferior performance of the home team. In games without fans, home teams created significantly fewer attacking opportunities and referee-bias was diluted when controlling for the attacking dominance of teams; such that the number of fouls and yellow cards ruled against away sides, while still significant, was reduced and no effects were observed for red cards. Implications for sporting practice and directions for future research are discussed.