I sort of get sports but I don't understand how people decide which team to like, especially when choosing a team that isn't the most local for them. They all seem the same to me.
Oftentimes it's because they saw something at an impressionable age. My dad grew up in NOLA, and due to the quirks of broadcasting (and before they had the Saints), they got all of the Green Bay games on TV. The first game he remembers watching was the
Ice Bowl and he got hooked, was a GB fan ever since.
Same with me, I was a casual football fan, but my freshman year of college my roommate was a big Patriots fan, and we saw the Cinderella story of Drew Bledsoe going down and Tom Brady stepping up and taking the team to a super bowl win, and it stuck with me and I got bigger into Patriots football (or jumped on the bandwagon, if you like).
My other sport, college basketball, growing up in CT EVERYONE is a college basketball fan because UCONN has always been so dominant (women) and in the 90s (men), plus Big East basketball is huge, almost like football to the SEC. Then I ended up going to another Big East school, and obviously then had a connection and have been a huge fan/supporter of my alma mater's team ever since.