Two silly premises
I simply cannot suspend disbelief on two premises of this movie, and yet I suppose I must have, because I enjoyed it and watch it each time it comes around on late night TV.
1. A night-club brawler forces his way into a professional sport, without any prior experience at the game, on his mean-ness alone. At a level where he is paid enough to give up his day job!! Sorry, sports take skills that need to be practised over years, from child age. Even in the early 60s.
2. He then falls for his land lady, an unglamorous widow with 2 ankle-biters to keep her crabby, who does not return his affection. Any pro sportsman has to work hard beating off hot young groupies, of whom he could take his pick for romance, sex or both. If he had an occasional romp with her when he wanted to stay home off the booze, that I could believe, but worshipping her in spite of her knock-backs, I can't.