Audio problem: Towards the end when Rubin Carter is in court, there are numerous occasions when you can hear the courtroom observers talking and whispering to each other. In the camera shots of the observers, there is not one person that is visibly talking.
Other mistake: In one flashback to a Carter-fight, while Carter is resting someone rubs his back with a sponge to cool him off. The sponge is dry when it should have been wet.
Other mistake: When Lesra is on the bus visiting Rubin for the first time you see a shot of him through the window. The bus is rocking and you can hear the engine (as though the bus is moving) but the reflection in the window remains the same.
Factual error: In the film, Carter leaves the military with service ribbons. In reality, he was discharged after being court-martialed.