Revealing mistake: During the movie's opening title sequence, Clubber Lang knocks out Jaffe in the sixth round. If you watch carefully, you can see that Lang's boxing glove actually hits Jaffe's shoulder, but he still knocks him out in the process.
Continuity mistake: When Rocky leaves the Jewish mausoleum on his motorcycle, he has no helmet. When Rocky arrives at his statue, he is now wearing a helmet.
Suggested correction: So he stopped either at home or a store and got a helmet.
Revealing mistake: When Paulie throws the bottle at the Rocky pinball machine at the beginning of the movie, the glass smashes but the bottle doesn't, indicating that the bottle is an obvious prop.
Suggested correction: Liquor bottles are small and dense and much stronger against damage than a thin sheet of plate glass.
Revealing mistake: Look closely after Thunderlips powerslams Rocky. Mainly when he pulls him up by the hair. Clearly that's not Sylvester Stallone but a stunt double.
Revealing mistake: In a shot of Clubber Lang and his manager standing in the corner at the end of the first round during the rematch between Lang and Rocky, "Clubber" on Lang's boxing shorts and "Heavyweight Champ" on the manager's shirt are back to front, indicating that it is a reversed shot.
Visible crew/equipment: During the second fight, there's a brief shot looking at the opposite side of the ring. A large motion picture camera and its operator are blatantly visible in the crowd.