Although Roberto Duran denies he said "no mas" during his famous return bout with Sugar Ray Leonard, most observers agree it was a combination of a fear of being knocked out and poor training that made the Panamanian fighter quit. Duran quit after Leonard dominated the fight for seven rounds.
Duran upset Leonard only five months earlier in a close decision. He celebrated by eating and drinking until his weight ballooned. When the date for the second fight was announced, Duran had to lose weight quickly. Boxing observers believe this caused the fighter to have stomach cramps in the second bout.
Leonard peppered Duran unmercifully throughout the bout. The flashy fighter played to the crowd and humiliated his opponent during the seventh round, right before Duran quit.
Duran originally said he was ill, then he claimed to have a shoulder injury. A later incantation of the story is that the referee misunderstood him and he never said "no mas." Duran's son, who serves as his interpreter, pointed out that it is very difficult for a fighter to speak with a mouth guard inserted.
For his part, Leonard reportedly believes that Duran did quit. Duran's failure to acknowledge that bothered Leonard for many years, but he reportedly came to peace and put the episode behind him.