Hammer (movie, 1972)

Hotheaded laborer B.J. Hammer can't go long without ending up in a fight, and, after he comes out on top in a particularly impressive workplace scuffle, word of his brawling skills makes its way to Davis, a top boxing manager. Hammer is hired by Davis and begins a lucrative career in the ring, only to find out that his new employer wants him to throw a fight and take part in other illicit activities. Hammer reacts to this news violently, and the feud is on.