Once upon a time, Billy (Jack Gyllenhaal Jake Gyllenhaal) was famous in the boxing circle for his fierce and ruthless left fist. For a moment, he was invincible and deserved the champion. However, when Billy loses his beloved wife Maureen (Rachel McAdams Rachel McAdams) in an accident, Billy begins to give up, giving up not only his career, but even alcohol and drugs. As a result, he is deprived of custody of his daughter Leila (played by Ona Lawrence Oona Laurence). Leila is sent to the welfare agency. Billy was gradually awakened by the departure of his daughter, who was so disappointed with his terrible situation that he decided to mend his ways. Hoping to get back on the ring, Billy finds coach Wells (Forrest Whitaker Forest Whitaker) and hopes he can help him take back what he has lost.