Kid Galahad (1937)

When a bellhop knocks out fighter Chuck McGraw, promoter Nick Donati realizes he's a potential champ. "Kid Galahad" justifies Nick's confidence, but Nick's mistress Fluff falls for him; in turn, the Kid falls for Nick's young sister. Now overprotective brother Nick turns against his new fighter, leading to a near-disastrous title fight and a murderous confrontation.