Challenge for Glory (1966)

A young ex-boxer has become a successful businessman, running his various enterprises with his best friend, another boxer whom he accidentally injured in a match. When the latter is found dead, he cannot believe it is suicide and decides to investigate. Sure enough, a group of gangsters is behind his death and, resenting his intrusion, try to ruin him and to pin the murder of his young friend's fiancee on him. At the last minute he shoots it out with the villains and emerges with his reputation intact.