Sport fandom has received considerable attention from social scientists, yet few have considered it from an evolutionary perspective. To redress this gap, we develop the hypothesis that team sports exhibit characteristics that activate mechanisms which evolved to facilitate the development of coalitions in the context of small-scale warfare. Based on this by-product hypothesis, we predicted a correlation between fandom and binding (i.e. group-relevant) concerns, especially loyalty. To test this prediction, we administered the Sport Spectator Identification Scale (SSI) and the Moral Foundations Questionnaire (MFQ) to 495 undergraduates. The MFQ measures three binding concerns, including loyalty, and two individualizing ones, harm and fairness. As predicted, fandom correlated significantly with loyalty (r = .27) and, within men, the two other binding concerns, authority (r =.22) and purity (r = .24). By contrast, fandom did not significantly correlate with harm or fairness. In addition, we predicted and found that men reported significantly higher levels of fandom (Cohen's d =.45) and loyalty (d = .27) than did women. In conclusion, this study presents data supporting the coalitional by-product hypothesis of fandom and should spur further research using fandom as a window into our evolved psychology.