Rocky III

In the three years since winning the world heavyweight title, Rocky Balboa has had a string of ten successful title defenses and has seen his fame, wealth, and celebrity increase. He even has time to participate in a friendly boxer vs. wrestler charity event against the world wrestling champion Thunderlips (Hulk Hogan). Meantime, Rocky's manager Mickey worriedly eyes a young and hungry contender rapidly rising through the ranks named James "Clubber" Lang. While unveiling a statue of himself at the steps by the Philadelphia Museum of Art, Rocky is publicly challenged by Lang, now the number-one contender. Lang accuses Rocky of intentionally accepting challenges from lesser opponents, and after he makes a sexual remark toward Rocky's wife Adrian, his challenge is accepted.
Mickey initially wants no part of it. Pressed by Rocky, Mickey admits he had handpicked Rocky's opponents to protect him from the beating he received in winning the title from Apollo Creed and to ensure Rocky remained successful and healthy. He tells Rocky that by becoming "civilized", he has lost his edge and that the young and hungry Lang would beat him inside of three rounds. Rocky manages to convince Mickey to train him regardless, but his Las Vegas-style training camp is filled with distractions and Rocky clearly does not take the challenge seriously, whilst Lang trains extremely hard.
Lang and Rocky meet at Philadelphia's Spectrum. A brawl breaks out backstage, and Mickey is violently shoved out of the way by Lang, causing him to suffer a heart attack. A now distraught Rocky wants to call the fight off, but Mickey angrily urges him on while he stays in the dressing room. By the time of the match, Rocky is both enraged and severely distracted by his mentor's condition. The match begins with Rocky pounding Lang with several huge blows, going for an early knockout, but the stronger and better prepared Lang is unfazed and quickly takes charge, dominating Rocky and knocking him out with a haymaker left hook in the second round, winning the heavyweight championship belt from Rocky. After the match, Rocky returns to the dressing room and witnesses Mickey dying. Kneeling at his side, Rocky speaks to Mickey, telling him that the match ended in the second round by a knockout, which Mickey misinterprets as a win for Rocky, shortly before succumbing to a heart attack.
Stopping by Mickey's closed gym, Rocky is confronted by his former nemesis, Apollo Creed, who witnessed the match as a guest analyst, and offers to help train him for a rematch with Lang in exchange for "a big favor." At first, Rocky is too demoralized to put forth his best efforts, which frustrates Apollo, but pulls himself together after Adrian helps him come to terms with Mickey's death. Apollo then trains Rocky at the gym where he once trained - Tough Gym in Los Angeles - and infuses Rocky's brawling style with more of the skill and speed that is Apollo's trademark.
The rematch takes place at Madison Square Garden. Apollo lends Rocky his American flag trunks that he wore during their first match. As the match is under way, Rocky sprints from his corner, fighting with a level of skill and spirit that no one, including Lang, expected. As a result, Rocky completely dominates the first round, demonstrating his new-found speed. After the bell rings, Lang is in a fit of rage over what has just happened and has to be restrained by his trainers.
In the second round, Lang gains the upper hand and Rocky adopts an entirely different strategy that bewilders Apollo by intentionally taking a beating from Lang, even getting knocked down twice but getting up both times before he is counted out while taunting Lang that he cannot knock him out.
By the third round, Lang, who is used to winning matches swiftly with knockouts in the early rounds, becomes increasingly furious over Rocky's taunts and quickly exhausts his energy trying to finish Rocky off with repeated knockout blows, which Rocky quickly begins to block or dodge entirely. With Lang winded and vulnerable, Rocky seizes the opportunity and throws his energy into increasingly damaging combinations on a winded and outboxed Lang, capping off with four huge straight left haymakers and a right hook to the head. As a result, Lang goes down for the count and Rocky becomes the heavyweight champion for the second time in his career.
Afterwards, Rocky fulfills Apollo's vague "big favor": a private rematch with him at Mickey's gym. However, this time they are fighting in the spirit of friendly competition rather than as fierce rivals. The film concludes with both of the fighters throwing their first punch simultaneously.

Question: What does Rocky tell Lang he cannot do to him?
Answer: Knock him out