Would you consider street dancing and breaking a sport?
I did a lot of that during my high school and uni years. Nothing gives me more adrenaline than competing and performing at dance parties.
If not, then I would say american football- both watching and playing. My friends and I usually have an annually game that we play around Thanksgivings just like the pros. lol
I like games of basketball too but I prefer to play football and get grass stains and torn shirts. Rafting at American River in Sacramento is also fun if you come with a large group and spending the whole day having water war with other groups. It's pretty hilarious shooting and knocking girls off their rafts...