-By Maitland McDonagh

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Embittered, broke and homeless, Iraq War veteran Tommy Conlon (Tom Hardy) turns up on the Pittsburgh doorstep of the father he hasn't seen in 18 years. Once a wife-battering drunk who coached both his sons to high-school wrestling acclaim by pitting them against each other in a bitter battle for attention and approval, Paddy (Nick Nolte) has sobered up and wants desperately to reconcile with his boys. But Tommy wants no part of Paddy's 12-step penance: He just wants a place to crash until he can get his bearings, which he finds at the local gym. Tommy isn't much for small talk or locker-room camaraderie, but after decking cocky MMA up-and-comer Mad Dog Grimes (Erik Apple) in record time, he's the instant alpha dog.

Paddy tries using Tommy's return to reconnect with his older son, Brendan (Joel Edgerton), a high-school physics teacher living in a pleasant, middle-class Philadelphia suburb with his wife, Tess (Jennifer Morrison), and their two little girls. But while Brendan would like to reconcile with Tommy, from whom he's been estranged since they were separated by their parents' ugly split (Brendan stayed with Paddy while Tommy went with their mother), he's just as uninterested in his father's amends-making. It's too little, too late and, anyway, Brendan has his own problems: Financially crippled by medical bills, he and Tess are about to lose their house. A moderately successful wrestler before the one-two of a life-threatening injury in the ring and Tess' pleas convinced him to throw in the towel, Brendan starts surreptitiously picking up extra cash in local fights.

When word gets out, he's suspended from teaching and, facing months of unemployment, Brendan is about to enter the underground fight circuit when he hears about Sparta, a big-money, high-profile Atlantic City-based tournament. He decides to go into serious training and try to qualify even though the odds are wildly against him: Even his old friend Frank (Frank Grillo), who's training his own Sparta hopeful, says as much. But an accident sidelines Frank's candidate and he agrees to train Brendan.

Tommy, meanwhile, has found his own road to Sparta: Unaware that a viral video of Mad Dog Grimes' beat-down has both made him an underground sensation and revealed his identity to a group of marines he anonymously rescued from certain death, he asks Paddy to train him, while making it clear that nothing is forgiven. He won't even fight as Tommy Conlon; he's going to use his mother's maiden name, Reardon. Tommy fights like a jackhammer, all raw power and inchoate fury that Paddy works to focus and refine.

Brendan is a dancer: tough but always aware—now more than ever—that speed, focus and strategic intelligence are his edge over sheer muscle, skills Frank helps him hone. Both dark horses make the cut, and their unlikely stories—the aging science teacher out to recapture youthful glory that wasn't even so glorious and the sullen loner who never let on he was a war hero until being outed by the men whose lives he saved—make for great color commentary and human-interest coverage. But can they actually go the distance?

Of course they can, but to the credit of director and co-writer Gavin O'Connor—whose credits include the documentary Smashing Machine: The Life and Times of Mark Kerr, which immersed him in the world of MMA fighters—there are plenty of unexpected—but not outlandish—twists along the way. And the outcome of the final face-off between brothers is both impossible to call and genuinely moving, in large part because Hardy and Edgerton (who are, respectively, English and Australian though if you didn't know, you'd never know it) are terrific actors, capable of bringing out the nuances in characters who could easily be reduced to types. Kudos are also due to stunt coordinator/fight choreographer JJ Perry: Nearly half the movie's 139 minutes is devoted to Sparta, and Perry's fight choreography is exceptional—you don't have to be a fan to follow the action or get thoroughly caught up in each match.