"I knew nothing about boxing when I started really," Gyllenhaal in the clip. "I knew that in order for me to pull it off in any way, I was just going to have to learn how to do it. When I set my mind to something I just won't stop until I do it. It's something I pride myself on. It's something I hate about myself. By the end I felt like I could do it."
Gyllenhaal fully committed, gaining 15 pounds of muscle for the role.
The movie follows fictional Junior Middleweight champ Billy Hope (Gyllenhaal) as he fights his way to a championship belt only to lose everything.
Rachel McAdams stars as Billy's caring wife Maureen, who is gunned down in front of him by another fighter wanting a shot at Billy's belt. Maureen's death sends Billy into a self-destructive, drug-addled spiral that leads the courts to take away his daughter (Oona Laurence). Making matters worse, Billy's income gets cut off after a doping scandal forces officials to suspend his boxing license for a year.