9. A cramp excuse
Roger Mayweather lasted significantly longer with Julio Cesar Chavez in their 1989 rematch than in their first fight, in which Chavez stopped Mayweather in two rounds. The second time around, Mayweather retired after the 10th round, citing stomach cramps as the reason for his inability to continue. Probably more likely it was the vicious body shots Chavez had been ripping in for 10 rounds that did it.