Inaccuracies
Possible spoiler:
There is always going to be some dramatic license taken, and it's pointless to watch a movie to find out "the real story." However ...
1. The trailer, at least, makes it look like Duran had to work hard after his loss to Leonard to come back and beat him. In truth, he first beat Leonard, then lost the second fight.
2. He is shown speaking English and understanding what others say to him. Duran does not speak English, or at least he didn't then.