Sport socialization research has revealed that a community is one of the most influential socializing agents. However, little is known about which aspects of a community promote sport socialization and how it occurs. In the current research, we identified and conceptualized two key factors characterizing sports teams’ fan communities, relative size and entitativity, and discussed how these factors influence sport socialization and its outcomes. First, we developed the model of community influence on sport socialization to depict the effects of relative size and entitativity on people’s perceptions and behaviors at the initial stage of their sport socialization. Second, we proposed the model of community influence on the outcomes of sport socialization, which explains how relative size and entitativity contribute to the outcomes of sport socialization.