Creator Breakdown: Scorcese was struggling with a cocaine addiction at the time and planning on retiring as a director. De Niro specifically brought the project to Scorcese in hopes that its themes of self-destruction would help Scorcese overcome his problems.
Dyeing for Your Art: Robert De Niro put on 60 pounds to play the retired Jake LaMotta, arguably starting the trend.
Playing Against Type: Joey LaMotta is played by Joe Pesci. Yes, that Joe Pesci. Of course, it was before he was typecast. Pesci still manages to start a fight by breaking a glass over someone's head, and ending it by slamming their head and shoulders repeatedly in a car door. He does apologize after, but only at the insistence of an old mobster.
It still counts, though, as compared to DeNiro, he's really the collected one. It's Jake that has the Hair-Trigger Temper.