We investigate to what extent crowd support contributes to the home advantage in soccer, disentangling this effect from other mechanisms such as players' familiarity with the stadium and travel fatigue. To evaluate the relevance of crowd support in determining home advantage we analyze same-stadium derbies (matches among teams that share the same stadium) in which teams enjoy different levels of support from the crowd – the home team has many more supporters, mainly because of season ticket holders – while teams do not differ in terms of travel fatigue or familiarity with the stadium. Our estimation results suggest the existence of a sizable crowd support's effect on the home advantage generated both through the influence on referee's decisions and through the encouragement of players' performance.