The Boxer (1972)

Boxer Teddy Wilcox (Robert Blake) leaves his manager and relocates. He finds Nick, a manager/trainer. Before Wilcox's first fight, Nick receives a threat-- Wilcox loses, or Nick will die. Despite Nick's efforts to sabotage the fight, Wilcox wins. Enraged, Wilcox orders Nick to keep away from him. Later that night, Nick is murdered. Of course, Wilcox is the primary suspect. Wilcox then tries to clear his name and find Nick's killer.