The film follows the story of Chuck Wepner, a liquor salesman and part-time boxer from Bayonne, New Jersey, whose life takes an unexpected turn when he gets the chance to fight Muhammad Ali for the heavyweight title. As a determined underdog, Chuck balances his demanding job, his tumultuous marriage to his wife Phyllis, and the rigorous training regimen required for the upcoming match. Surpassing everyone's expectations, Chuck pushes himself to the limits in an attempt to seize his shot at greatness, generating significant media attention and local support.

After the high-stakes fight, Chuck's life spirals in unforeseen directions, affecting both his personal and professional world. The impact of sudden fame and the pressures of living up to a new public image start to weigh heavily on him. Struggling with various internal and external conflicts, Chuck faces significant challenges that test his resilience and character. Throughout this journey, he copes with the unintended consequences of his newfound status while seeking redemption and a sense of personal fulfillment.