The Champ(1979)

Overview:

Billy used to be a great boxer, but he's settled into a hardscrabble life that revolves around drinking, training horses, and the one bright spot in his existence — his young son, T.J. Although Billy has had custody of T.J. since his wife, Annie, left the family years ago, her return prompts a new struggle for the former fighter. Determined to hold on to his son, Billy gets back into the ring to try and recapture his past success.