Sumo Wrestling was a chapter in the book Freakanomics and the authors found statistical proof that Sumo's actually do throw fights. It's because tournaments are based on a points system, and if a sumo qualifies for the next round with matches still to fight and comes up against someone they train with, in their 'stable', a friend, etc, they lose those matches a larger % of time then if they come up against those sumo's in earlier, points critical matches.
Yeah, I'm a statistics and probability nerd