Chess boxing has evolved from a performance art piece to a serious worldwide professional sport. Two competitors engage in six rounds of chess and five rounds of boxing, switching between the two every three minutes. A player can win by knockout, technical knockout, or checkmate, or if his opponent resigns, exceeds the time limit, or is disqualified. If both the contests end in a draw, the player of the black pieces wins.
In football tennis (below), you have to return the ball over the net without using your hands. Up to three players can play on each side, with corresponding rules regarding the number of touches and bounces allowed on each return. This sport is growing too — the first rules were written in 1940, and it held its 11th world championship in 2014. Now we need a way to combine all four of these.