Kelly the Second (1936)

Lunc- counter manager Molly Kelly gets into an altercation with truck driver Cecil Callahan that lands him in jail. After seeing his fighting skills, though, Molly and her boss, Dr. Klum, decide to turn him into a prizefighter. Together they have great success, thanks in no small part to Molly's unorthodox training techniques. Eventually Callahan is good enough to challenge the heavyweight champion, but jealousy may intervene.