The Set-Up (movie, 1949)

Stoker Thompson is a 35-year-old has-been boxer. His once-promising fighting career has come crashing to the end. Tiny, Stoker's manager, is sure he will continue to lose fights, so he takes money for a "dive" from a mobster, but is so sure that Thompson will lose that he doesn't tell the boxer about the set-up. At the beginning of the last round of the vicious boxing match he learns of the fix.