I did cross country and track and field in high school. Very positive uplifting people. Not the "popular" crowd, and I found cross country people were usually very intelligent on average.
It did wonders for my social life, self-esteem, and for developing social skills more.
When I was younger, my grandparents gave me tennis lessons and I have always enjoyed tennis. I'd probably join in on playing any sport just for fun when I'm in a group of people (particularly because then I don't have to use my social skills as much).
I am also quite an active INTP, but in thinking about it, I'm probably only active because I "should" be active and I force myself a lot of times to get up and do stuff.
I realized the other day though why I prefer walking to running. When walking I can think better! haha! Running takes up more of my concentration, especially if I'm trying to push myself. If I'm running, and I don't concentrate on my running at least partially, I will usually start running pretty slowly, thereby defeating the purpose of running in my opinion (getting a good workout in--for health purposes, both mental and physical). I do not really like running, but it does make me feel better.
I'm not even sure why I did cross country in high school, but I think partially it was because I was going to join the tennis team, but missed tryouts. Then when I heard they were still taking people for cross country (as there is no limit), I thought, "Why not? I'm pretty fast."