Most commonly by the geographic area one lives in or has ties to. Otherwise, some people like to choose a team that wins a lot or, on the opposite side, an “underdog” team that never wins.
Yup, that’s me. I grew up near Seattle, so the Mariners and Seahawks are my teams for baseball and football. I got into soccer after I moved to Utah and the Sonics left Seattle, so Real Salt Lake and the Utah Jazz are my teams for soccer and basketball. We didn’t have a hockey team growing up, so I went for the Vancouver Canucks for hockey, but now I’m going for the Utah Hockey Club.
I used to really like the As because of Moneyball, and if I’m watching a game with other teams, I go for the underdogs (e.g. for the Premier League, anyone other than Man U, and I’m partial to Arsenol because they have a cool name).
Geolocation or affinity to location, significant player from region playing at team, family inherited “not ok to not like team xyz”, stats, position (underdog, champion) etc
Like a religion, or culture. As other have said, location, family, etc. Also, advertising plays a role, and then there are people who get really into it and spend a lot of time focusing on different teams, and sports, until they just become team/sport agnostic or focus on the one that meets their statistical, and business practices, requirements.
In addition to the other reasons mentioned, I’ll add simply going to a home game for a specific team as an introduction to a sport. For example, I live in an area with multiple high level college sports teams. I went to my first college basketball game at age 11 at one of these schools, so I was their fan for a long time after that. Last year we went to visit the town where my wife’s dad is from. They have a professional team for a sport I enjoy but really only watch at the international level. I had no pro team I follow in that sport, but they were in playoffs while we were there. At that point we didn’t get tickets but I was watching on TV and I enjoyed watching, so I found a way to watch more at home. If we ever go back I’m pretty sure my wife’s cousin will get tickets so we can go. I did get a shirt for the team before we left.
First step is to forgo a distinct personality.
