1. Ohio State Football - I still recall watching games every Saturday with my Dad...him yelling at the TV in frustration during the John Cooper years. The funniest part is I've adopted every one of his tendencies without even realizing it until my wife pointed it out last season - yelling at the TV, making outrageous accusations about the officials pulling for the other team, getting unnecessarily angry without no one in particular. I honestly hope I can share this experience with my kids one day...for now it's just my wife rolling her eyes and my dog getting nervous when I jump up and start yelling at the TV with no warning.
2. Golf - I know this is very general, but again comes back to spending time with my Dad and brother. We watch it on TV together, go playing together, and now that we're all older can travel to some of the major tournaments together and every few years take a long golf trip together. It's all added to a lot of bonding time that otherwise might not happen.
3. New York Yankees - while my parents were both born and raised in Youngstown (we all moved when I was 5 to the east coast), my Dad has had random favorite teams. He loved Micky Mantle so was a Yankees fan and Bart Starr so followed the Packers. We've gone to many games together throughout the years and has again added to shared experiences that we can look back on.
I guess it's not surprising, and I'm sure many with have similar sentiments, but the passion comes not just from the sport/team itself, but from those we share those experiences with.
Great thread, and glad I got to relive some memories.