There's no percentage in smartenin' up a chump

The Set-Up (1949)

Suggested by Ian Culbard (kinda it was a twitter mention so not a direct recommendation  hence no intro).

A solid, mostly gripping boxing thriller with the interesting premise of a fixed match except the boxer doesn't know it. It spends half it's short time setting the scene, giving us snippets of other boxers whose matches we never see and who have little impact on plot but create a vivid, compelling world, each pushing Robert Ryan's unwitting chump towards an inevitable but still satisfying decision.
The match itself, taking up most of the rest of the film, is exciting. Simple but strikingly shot, packs power even 60 years on.