I didn't have too many friends who were in organized sports as kids. My best friend's dad, though, put a lot of pressure on both daughters to play soccer for the sake of soccer scholarships (mom was a bit saner in that regard--she thought it should be fun). Both were also in taekwondo. My best friend in particular had a number of ankle sprains that basically meant that by the time we graduated, she couldn't participate in either anymore. And most of these sports are pretty physically and/or technically demanding and aren't the sort of thing that one returns to later on (at least, most of the time).

Jr. high PE classes were what drove me to hate physical activity, actually. Run 3 miles, no walking, or you get a C for the day? Come on. But then, the only organized sport I participated in was fencing, which was thoroughly awesome. I'd like to go back, but a) I was really bad at it, and b) it's really expensive, and finding an organization is not the easiest thing in most cities.