In 1975, the heavyweight boxing world champion, Apollo Creed, announces plans to hold a title bout in Philadelphia during the upcoming United States Bicentennial. However, he is informed five weeks from the fight date that his scheduled opponent is unable to compete due to an injured hand. With all other potential replacements booked up or otherwise unavailable, Creed decides to spice things up by giving a local contender a chance to challenge him.
Creed selects Rocky Balboa, a journeyman southpaw boxer who fights primarily in small gyms and works as a collector for a loan shark. Rocky meets with promoter George Jergens under the presumption that Creed is seeking local sparring partners. Reluctant at first, Rocky eventually agrees to the fight which will pay him $150,000. Rocky undergoes several weeks of unorthodox training, such as using sides of beef as punching bags.
Rocky is later approached by Mickey “Mighty Mick” Goldmill, an aging former bantamweight fighter turned trainer whose gym Rocky frequents, about training him further. Rocky is not willing initially, as Mickey has not shown much interest in helping him before and sees him as a wasted talent, but eventually accepts the offer.
Meanwhile, Rocky begins to build a romantic relationship with Adrian Pennino, who is working part-time at a pet store, culminating in a kiss. Adrian’s brother, Paulie helps him get a date for his sister and even offered to work as a corner man with him, becomes jealous of Rocky’s success, but Rocky placates him by agreeing to advertise the meatpacking business Paulie works for as part of the upcoming fight. Rocky turned him down. The night before the fight, a sleepless Rocky visits the Philadelphia Spectrum and begins to lose confidence. He confesses to Adrian that he does not believe he can win, but strives to go the distance against Creed, which no other fighter has done, to prove himself to everyone. That is he can go the distance and still standing he won’t be another bum from a neighborhood.
On New Year’s Day, the fight is held with Creed making a dramatic entrance dressed as George Washington and then Uncle Sam. Taking advantage of his overconfidence, Rocky knocks him down in the first round—the first time that Creed has ever been knocked down. Humbled and worried, Creed takes Rocky more seriously for the rest of the fight, though his ego never fully fades. The fight goes on for the full fifteen rounds, with both combatants sustaining various injuries. Rocky, with hits to the head and swollen eyes, requires his right eyelid to be cut in order to restore his vision. Apollo, with internal bleeding and a broken rib, struggles to breathe. As the fight concludes, Creed’s superior skill is countered by Rocky’s apparently unlimited ability to absorb punches, and his dogged refusal to go down. As the final round bell sounds, with both fighters locked in each other’s arms, they promise to each other that there will be no rematch.
After the fight, the sportscasters and the audience go wild. Jergens announces over the loudspeaker that the fight was “the greatest exhibition of guts and stamina in the history of the ring”, and Rocky calls out repeatedly for Adrian, who runs down and comes into the ring as Paulie distracts arena security. As Jergens declares Creed the winner by virtue of a split decision (8:7, 7:8, 9:6), Adrian and Rocky embrace and profess their love to each other, not caring about the result of the fight.