Christian Bale got involved when Mark Wahlberg asked him to take part in the movie. Wahlberg and Bale knew each other through their daughters, who attended the same elementary school.
Mark Wahlberg waived his own salary, and took no upfront fee for this film. Christian Bale was paid only $250,000 for his role.
Micky Ward's real-life trainer Mickey O'Keefe was asked to appear as himself in the film, but turned the role down, since he had never acted before. Mark Wahlberg told him he would be able to, since he was a cop, and therefore he has to act and think fast on his feet. This was convincing enough, and he took the role.
Christian Bale spent hours with the real Dicky Eklund to learn how to emulate him properly. He had to lose 30 pounds because Eklund was a crack addict at the time. Director David O. Russell said it was much more than mimicry. He remarked: "Dicky has a rhythm to him, a music. Christian had to understand how his mind works."
Mark Wahlberg began training for the role in 2005. Throughout the various production delays, Wahlberg continued to train every day so that he could be ready for filming. Filming finally began in July 2009.