Overall, I'd have to agree with Asmodai and say soccer. I mean, never mind their physical strength to deal with the rough and tumble players from the opposing teams when they're all going for the ball, but there's also the cardiovascular aspect. These players stay on the pitch for some serious stretches of time, and they're running the equivalent of several kilometers over the course of a match. With hockey, American football, baseball, etc., the actual gameplay usually only goes for 2-3 minutes at a stretch before a time out, or a "break" between plays while strategies are devised, players are switched, etc. There's also the "eye-foot" coordination that soccer players need when they try to score a goal.