The Ballyhoo Buster(1928)

Bob Warner sells some cattle to two men who later drug him and rob him of the sale money. He takes a job with a medicine show as a barker, offering a reward to any spectator to last three rounds in fighting him. While in the ring, he notices in the audience the two men who stole his money. He knocks out his contestant, pursues the crooks, and recovers the money.