Crowd Roars, The (1938)
Not to be confused with the 1932 film (starring James Cagney as a race car driver) of the same name.
Quick summary - a boxing movie about a young boy with a deadbeat father that, under the tutelage of a boxing champion, becomes a successful boxer himself until he kills his former mentor (trying to make a comeback for financial reasons) in the ring. He then tries to give up the game but is lured back into it by financial need of his own and a gambler whose daughter he falls in love with, only to be imperiled by his father's loose lips about the gambler's secret.
Later remade, almost shot for shot, as Killer McCoy (1947) except that Mickey Rooney played both the young and the older Tommy McCoy character. Click the link (above) to see the plot details. This original was directed by Richard Thorpe. Another change, besides the actors themselves, is the way in which Tommy and Sheila begin dating - in this one, Jane Wyman is a friend of Sheila's that invites Tommy to their private girls school dance; in the remake, Tommy takes Sheila out for a date after his fight with Sailor Graves. Plus, young Tommy (Gene Reynolds) is a solo pre-fight singer when he meets his boxing mentor Johnny Martin in this film whereas Mickey Rooney's Tommy does a dance act with his father in the remake (and the impetus for Tommy going into the ring to fight is due to his father's bet in the former vs. a newspaper selling dispute in the latter). Lastly, 10 (vs. 5) years pass between the beginning and the "present day" parts in this one (vs. the remake).
The cast differences from Killer McCoy (1947) include Robert Taylor as "Killer" McCoy, Frank Morgan as his father, Edward Arnold as Jim Cain (the gambler), William Gargan as Johnny Martin, Lionel Standler as Happy (the trainer), Maureen O'Sullivan plays Sheila, Nat Pendleton plays the gangster that Cain scams, and J. Farrell MacDonald as Father Ryan. I'm not sure which version I prefer, both are above average with capable casts and a compelling story.