Continuity mistake: In the scene where Stallone gets hit by the UFC fighter, he doesn't see the hit coming because he gets hit from his right side. Later on, when driving his girlfriend home from the restaurant, he is still blind in his right eye and doesn't see the car coming from the right. However, during the Grudge Match, he is suddenly blind in his left eye.
Other mistake: Originally when BJ introduces himself to Kid, he acts as if he can't recognize him. However, later on Kid gives BJ a scrapbook showing he has followed him all these years and would definitely know what he looks like.