Muhammad Ali Rematch:
Liston was hit by what looked like a soft punch and considered KO.

Ref: http://en.wikipedia.org/wiki/Sonny_Liston

The ref given above makes it look official. This is what I think happened:

The Italian Mafia (who he worked for as a bone crusher) took illegal bets on the fight then fixed the fight to make more money.

"Many believed the fight was fixed. George Chuvalo, who sat in the fourth row at ringside and later fought Ali twice, said, "It was a phony." Floyd Patterson also said he did not believe the fight was on the level, as did former heavyweight champions Jack Dempsey, Gene Tunney and Joe Louis" - Wikipedia