The onside kick. It's one of the most polarizing and exciting plays in all of sports. If done correctly, it can turn the momentum of the game on its heels, as demonstrated by the Saints in Super Bowl XLIV. But on the opposite dime, it can destroy a teams' chances by giving the opposition prime field position.
According to my count, 66 onside kicks were attempted last season in the NFL. Only nine of those panned out. That's about a 14% success rate. Given that sad statistic and the tendency of the onside kick to backfire, it's no wonder why we seldom see the play called upon, and only used as a last resort in the dying moments of a game.