MMA may be considered the world's fastest growing sport according to some, but the hottest sport has got to be CheckersWrestling, er, ChessBoxing.  Check it out.

From Wikipedia, the rules are as follows:  A match between two opponents consists of up to eleven alternating rounds of boxing and chess sessions, starting with a four-minute chess round followed by two minutes of boxing and so on. Between rounds there is a 1 minute pause, during which competitors change their gear. The form of chess played is "speed chess" in which each competitor has a total of twelve minutes for the whole game. Competitors may win by knockout, checkmate, a judge's decision or if their opponent's twelve minutes of chess time elapses. If a contestant doesn't make a move in the chess round, he will be issued a warning by the referee. At the second warning the contestant will be disqualified.

This sport is going to pave the way for innumerable hybrid sports, don't you think?