I know of one bout Rocky Marciano failed to win and that was against Welsh legend Dr Jack Matthews, Matthews and Marciano fought out a 4 round draw, Marciano was a serious amateur boxer, Matthews wasnt he only had a few bouts, all observers thought that Matthews had won but because it was a frieindly match and the Welsh and the Americans were allies during WW11 they called it a draw. Its lucky that Marciano did not try and take Matthews on at rugby, Matthews broke a NewZealand All Black players sternum and ribs in a tackle ! , the All Black came back on the pitch to score the winning try, to describe these men as hard is an understatement, and im not talking about Marciano im talking about Dr Jack Matthews and Ron Elvidge.
Maciano has lost 1 Amateur Fight its true vs Henry Lester . The fight was on 15 April 1946 in Fort Lewis Washington.Rocky Marciano was disqualified for an illegal Punch in the third round - it was the only Lost - Disqualification in his boxer career.But in his Professional HW Carrer Marciano is undefeated.