I don't typically watch sports particularly regularly or with particular interest, but there is one sport that I will always watch, including (at least trying) to get up at 3am to watch the finals happening live in Australia.
That's tennis. I think it's just happy memories, because my mom watched it when I was very young and she wasn't working so she could take care of me, and I was interested in whatever she was interested in, so those "happy childhood memories" are still warm and fuzzy today. That may be why others are so interested in other sports.
Heaven knows it's not like I'm good at it myself or anything. Playing well involves several different learned skills that don't tend to be what you'd just do on your own--the way a beginner hits, with no knowledge, is never going to turn into skill because the right way is not intuitive.
I also like that it is a sport that features the individual rather than the team--the stories are to me more interesting that way. Also, as long as the William's sisters aren't playing, the women's game is just as interesting, and tends to be nearly just as highly regarded and watched, as the men's game. Not just the female segment but the entire tennis world seems almost as interested, which is really quite spectacular considering how widely un-interested the rest of the world is in the rest of the world's women's sports. Tennis is even the only sport I know of that includes an event in which men and women play with and against each other (mixed doubles.) Also tennis is one of those sports that does not have a set time limit, rather, you play until you reach the end based on the point system. If that takes eight hours, well, then it takes eight hours. To win you have to really want it and be willing to fight long and hard for it.