How/Why did you become a fan of whichever teams you’re a fan of? As for me:
MLB
I’m a life-long Chicago Cubs’ fan. I joke that it was a rule in our house growing up, that my Mom would boot us out if we didn’t root for the Cubs, and I was too young to get a job. That’s not entirely true, though. Mom’s a Cubs’ fan, as are all of us kids, but she’s also a Bears’ fan and has no trouble with her kids not being Bears’ fans. So, while I’m sure my Mom being such a huge fan had a lot to do with my leanings, I think some of the blame falls on WGN. As a kid (starting circa ‘82), the Cubs were on TV all the time, during the day. We also got KTLA (Dodgers) and KSOMETHINGOROTHER (Mets) on our local cable, but they played a lot more night games. My Dad was home at night, and isn’t into sports, so we rarely watched a night baseball game. So, I’d say I’m a Cubs’ fan because of Mom (70%), WGN (15%) and day baseball (15%). Harry’s 7th inning stretch didn’t hurt.
NFL
Again, Dad’s not into sports. When he was home on Saturdays and Sundays, Mom would watch football with the sound turned down, and Dad would listen to Connie Francis records and the like. Because of this, I never really understood football. For years I thought the whole point of the game was the dog-pile. I could never really see the ball, and without the benifit of sound, I had no idea what was going on. But then…
My Mom’s youngest sister dated and then married Steve. Steve is possibly the biggest Cowboys fan I’ve ever met. While my aunt and Steve were dating, he spent a lot of time at our house. Dad liked Steve, and would normally let him watch the 'Boys if he was around on weekends, Thanksgiving etc. I was 11 or 12 and thought Steve was the coolest guy ever (still do). So, I hung out with him whenever I could, including during football games, and he helped me understand the game, which I never had before. Learning how to watch football with a Cowboys fan, and wanting approval from the Coolest Uncle Ever on top of that, I’m still a fan of the Cowboys.
NHL
I never watched hockey until I dated a hockey fan. Now that we’ve split up, I don’t watch much hockey anymore. But, during the time we dated he informed me that I needed to pick a team, but it couldn’t be his team, The Bruins. We didn’t like the same baseball or football teams, and it was a fun rivalry between us in those 2 sports, so why not hockey, too?
I didn’t pick a team right away, but one night after work, at 4 in the morning, a great ESPN /NHL commercial came on. There was a hockey player skating slowly along, saying something to the effect of “It’s just a mascot, no big deal” (I don’t remember what he said vebatim). They stop the tape and roll it backwards, and a deep, evil sounding voice says, “We are the Devils. We are Pure Evil.” I’ve been a Devils’ fan (though, not a good one) ever since.
NBA
I couldn’t care less, but I root for the Bulls because my brother’s a Bulls fan. And I root for Golden State, just because I’ve never met another Golden State fan.
NCAA
I root for the NMSU Aggies, since they’re the home team. But since they pretty well suck in every sport execpt golf, and they’re very rarely televised, I root for other teams as well.
I like Michigan, because my brother’s a huge fan, and I ended up with all the Hand Me Downs when he was still growing (they were actually Hand Me Ups, as he’s 4 years younger than I, but also much bigger and taller). I figure, since I’ve got the gear, I may as well root for the team. I also like Penn State, for no particular reason, except I think they have a cool name.
So, how about you? Feel free to add in other sports (soccer, tennis, golf etc).