Here are some differences: sports fans don't think that their team is capable of supernatural feats. I don't think I've ever seen a fan of one team try to convince a fan of another to change allegiance, or proselytizing on a street corner. Sports fans know that the teams of the other fans exist, while religious people usually deny that other gods exist. Similarly, religious people don't have to worry about whether Yahweh could beat up Vishnu, but sports fans get to actually see what happens when their teams compete.