In the near future, human boxers have been replaced by robots in the sport of boxing. Charlie Kenton, a washed-up fighter, tries to make a living by piecing together low-end robots and taking them to underground fights. His luck seems to go from bad to worse until he learns that his estranged son, Max, needs a guardian after his mother's death. Charlie reluctantly agrees to take Max for the summer in exchange for money, and together they discover a discarded robot named Atom in a junkyard. Max, fascinated by Atom, insists on fixing him up, and eventually, they enter Atom into competitions.

As Atom starts winning fights, Charlie and Max begin to bond, and Charlie's enthusiasm for the sport is reignited. Atom's unexpected success leads to bigger opportunities, drawing attention from top-tier competitors who want a shot at defeating the underdog robot. Along the way, both father and son confront old wounds and learn to work together, discovering the true meaning of family and resilience.