A troubled Marine, Tommy Riordan, returns to his hometown of Pittsburgh and enlists his father, Paddy, a recovering alcoholic and former MMA trainer, to prepare him for a winner-takes-all mixed martial arts tournament called Sparta, which carries the largest purse in the history of the sport. Tommy's estrangement from his father and older brother, Brendan, who was a former fighter himself, is palpable. Paddy, seeking redemption for past mistakes and yearning to reconnect with his sons, trains Tommy with relentless fervor, as Tommy becomes a dark horse in the fight world with his impressive and aggressive wins in the ring, harboring his own deep-seated reasons for entering the tournament.

On the opposite side of the spectrum is the Marine’s brother, Brendan, a high school physics teacher and former UFC fighter struggling to provide for his family. Facing financial distress, Brendan begins to fight in small-time bouts to make extra money. His desperation leads him to consider the Sparta tournament despite the risks involved with returning to a professional fighting career. With the prize money large enough to solve his financial problems, Brendan is driven to succeed and starts training under an old friend. As the tournament approaches, the brothers' paths are set on a collision course that will have them confront their shared past and the deep rift that has developed between them.