Raging Bull

The story of Jake LaMotta, a former boxing champion whose reputation for tenacity and success in the ring was offset by his troubled domestic life. Not so much a film about boxing as an exploration of a man with paralysing jealousy and sexual insecurity which, in the end, left him destitute, alone and seeking redemption. The film is renowned for the mix of structure and creative flexibility, which led to unique improvised scenes.
This was the first Martin Scorsese film edited entirely by Thelma Schoonmaker (1940) and it won her an Oscar for Best Film Editing. She has since worked with Scorsese on every single film.
"Editing is a lot about patience and discipline and just banging away at something, turning off the machine and going home at night because you're frustrated and depressed, and then coming back in the morning to try again." (Thelma Schoonmaker)