In the city of Lowell, Massachusetts, Dicky Eklund (CHRISTIAN BALE) is a boxing legend, having gone the distance long ago with none other than Sugar Ray Leonard. Now, his younger half-brother, Micky Ward (MARK WAHLBERG), is trying to follow in his prize fighter footsteps. The only problem is that those in his corner, despite their best intentions, aren't good for his career.
While Micky's dad, George (JACK McGEE) is supportive, he must take a back seat to the brothers' mom, Alice (MELISSA LEO), a strong-willed woman who serves as her son's manager but doesn't always book him against the best opponents, either for his career or health. And although local cop Sgt. Mickey O'Keefe (MICKEY O'KEEFE) helps as Micky's trainer, the boxer relies on his older brother for all of his physical training, tactics, advice and more.
The big problem, however, is that Dicky has quite a record with the local police and is now a crack addict, meaning he's always late, if he even shows up at all, for his brother's training. With a series of recent losses, Micky is ready to throw in the towel, but his new girlfriend, local bartender Charlene Fleming (AMY ADAMS), tells him he needs to get away from his family in order to succeed, putting her at odds with Dicky, Alice and her many adult daughters. With his career suddenly on an upswing, Micky must decide who he wants in his corner.