Every actor has a different way of preparing for a film role.
Anthony Hopkins has said it's simply about memorizing his lines and hitting his marks. Others, however, take preparation to a whole different level. The real Carter was on his way to boxing greatness in 1966 when he was wrongfully convicted of murder. It was probably a year and a half prior to shooting that I started training. I worked out hard every day, probably six, seven, eight hours a day sometimes, in boxing training in preparation.