United States Marine Corps Tommy Riordan (Tom Hardy) visits his father, Paddy Conlon (Nick Nolte), a recovering alcoholic who has returned to his Catholic faith. Tommy had to run away from Paddy with his dying mother when he was just a boy due to Paddy having previously been an abusive alcoholic, and has never quite forgiven him. Paddy tries to convince him that he has changed, but to no avail. The next day, Tommy enters a gym where, in less than a minute, he beats unconscious a professional fighter named Pete "Mad Dog" Grimes (Erik Apple), in a fight which is filmed with a cell phone and later uploaded to the internet, where it goes viral video. Tommy learns about a winner-takes-all mixed martial arts tournament called Sparta in which the winner will receive $5 million. Tommy asks Paddy to help him train for the tournament, but only under the condition that Paddy does not try to reconcile their relationship.