The so-called octagon of mixed martial arts — the caged arena in which bouts take place — has a long way to go in movies if it wants to approach the cinematic power of the boxing ring.

Brightly lit and enclosed by wire mesh, it more resembles a giant chicken coop than a solemn battlefield. In the movies, one expects something fearfully referred to as The Octagon to be a James Bond villain modelled after Buckminster Fuller.

But in Warrior, director Gavin O’Connor has turned the octagon of Ultimate Fighting into a cage of boiling family emotion. Though the film might seem an inconsequential fight movie complete with tough guys and tattoos, it turns genre fare into a surprisingly moving father-and-sons melodrama.

Nick Nolte — back in his wheel house as an aging, reformed drunk — plays Paddy Conlon, the father of two sons, both of whom are estranged from him. Years ago, Paddy was a violent drunk whose abuse drove his wife and Tommy (Tom Hardy) to flee Westward. The older son Brendan (Joel Edgerton), hoping to remain close to his father, stayed and married his teenage sweetheart (Jennifer Morrison). The brothers, too, separated for good.

The younger and brawnier of the two, Tommy, appears suddenly on Paddy’s Pittsburgh stoop. A former Marine and high school wrestling star, he proposes to reunite with his father so that he can be trained “the old regimen” as he becomes an MMA fighter.

Tommy repeatedly makes clear that he wants his father’s help only in training: “This doesn’t mean anything,” he says.

Brendon has made out better in life than Tommy. He has two girls, a suburban house in Philadelphia and teaches high school physics. But the bank is threatening to foreclose on their house, and Brendan’s second income (fighting mixed martial arts in parking lot tournaments) has gotten him suspended from teaching.

Set in working class Pennsylvania, Warrior has plenty of contemporary resonance. The Conlon brothers have both been dealt an unfair lot: Tommy an aimless Iraq war veteran, Brendan squeezed out by an unfeeling bank.

They each, separately, turn to mixed martial arts as their lone avenue of recourse, and each gets into an ESPN-televised tournament in Atlantic City dubbed ‘Sparta,’ in which the prize is $5 million.

The set-up is trite, but O’Connor (who wrote the script with Anthony Tambakis and Cliff Dorman) works hard to layer it in details. Much of the film feels calculated and overdone: the grim industrial blight, the hooded sweatshirts, Paddy listening to Moby-Dick as an audio book.

Similar to O’Conner’s last film, Pride and Glory, a police family drama, the director gives epic, self-serious treatment to a plot built on cliches. Both films, though, take familiar tropes (the corrupt cop story, the sports underdog) and imbues them with family tragedy and haunting pasts.

On the whole, the 139-minute Warrior works better because of its outsized ambitions.

The acting helps the film’s realism. Hardy (Inception, Bronson) is boiling with rage, a bull with his horns lowered for the entire movie. Edgerton (Animal Kingdom) is more composed, but each carries a slight darkness. Their physicality (which is easily up the film’s rigors) comes across best in non-fighting scenes, where they move gingerly, like fighters.

Nolte adds at least one weight class to Warrior, playing the ultra-weary Paddy, a broken man who accepts his sons’ ill-treatment because he knows he deserves it. Supporting work from Kevin Dunn (as a sympathetic principal) and Frank Grillo (as Brendan’s trainer) is also solid.

By the time Warrior builds to its championship finale, the sadness of the Conlon brothers is riveting. They battle brutally, punishing themselves, unable to break the chain of violence begun by their father, who watches mournfully from outside the claustrophobic cage.