I usually look to Vonnegut when the fan noise gets to be too much. But here’s a good explainer:

A sports team is an expression of a fan’s sense of self, as I learned from dozens of interviews and research articles I surveyed for my book “The Secret Lives of Sports Fans,” is an expansion of a fan’s sense of self. It is not an obnoxious affectation when a devotee uses the word “we”; it’s a literal confusion in the brain about what is “me” and what is “the team.” In all kinds of unconscious ways, a fan mirrors the feelings, actions and even hormones of the players. Self-esteem rides on the outcome of the game and the image of the franchise.

The psychology of why sports fans see their teams as extensions of themselves