Canvas Back Duck (1953)

Donald and his nephews are visiting the carnival. After Donald makes a relatively high score on a weight testing machine, he is thought to be a veritable strong man and takes on an offer from a little boy to fight his uncle in a boxing match. Unfortunately for Donald, that "little boy" is actually a con man in cahoots with boxer Peewee Pete who is anything but what his name implies. His nephews notice and try to warn Donald but he finds himself in the ring with Pete anyway