Out of the major sports, baseball.
Football - I can probably run the ball for a yard or a couple at most, before getting crushed. Still, as long as I have a solid line and a good play I can rush the ball.
Basketball - I can make a basket. I wouldn't make a lot of them, but I can throw it up and am capable of making a basket. I know I'm not dribble king and would pass a lot, but if someone gave me the ball I can make a shot real quick.
Boxing - As long as it's in my weight class anyone has a punchers chance. Given I couldn't go more than 3 rounds and would just collapse from exhaustion (if I made it that far) I still have the chance of landing a shot.
Hockey - The puck is in front of me. I'd take slot shots all day and eventually I would make a goal. Same with soccer.
Baseball - No chance in hell. It's different when a 97mph fast ball or 85mpg screw ball is coming at you. I wouldn't even be able to make contact. Even if I did, more than likely it would just be an easy out. You think you even have a 25% chance of getting a single. Well, you might as well go to a triple A farm team and wait to be called up to the majors on an injury because you are batting .250 which really isn't all bad.
All the other major sports I at least can have an impact. Rush 2 yards for a TD or for a 1st down before getting pummeled. Make a basket or a couple free throws. Land some good punches. Baseball the average person would just look like a clueless idiot.