That's water polo. Polo is like croquet on horses. Well, without the holes you have to get it through. There's only one ball and four players on each team (three if you're doing arena polo) and they have long mallets to hit the ball with. The idea is to score on the other team's goal. I've never played, but I watched a couple matches before. There's some stuff during the summer olympics. Dressage, show jumping, and eventing. A lot of horses doing tricks and jumping. It's probably not really interesting if you're not into that sort of thing. But there's also the races and rodeo.
I haven't thought to look into it. Thanks. I'm not sure how I'd have made up for it if you didn't.