During an underground fight, a man named Jax discovers his opponent is fighting dirty by wearing brass knuckles. His coach urges him to walk away, reminding him there are no rules and even champions can be destroyed. Defiant, Jax insists on fighting, recalling his coach's past lesson about an unbeatable heart leading to unbeatable punches. The coach, while acknowledging Jax's spirit, doubts his readiness, pointing out that Jax's years in prison have left him out of practice and physically unprepared for the brutal match ahead.