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 through the encouragement of players’ performance. Furthermore, we find consistent evidence that the support of the crowd tends to bias referee’s decisions (in terms of penalties, red cards, and yellow cards) in favor of the home team.