Continuity mistake: When Mr. Miyagi saves Daniel from the Kobra Kai during the night of the Halloween dance, Mr. Miyagi flips Johnny to the ground and only strikes him in the stomach. The next morning, when Daniel and Mr. Miyagi go to Kreese's dojo, Johnny is seen with a black eye. Very hard to get one since he was never hit in the face.
Suggested correction: When Miyagi dropped him, the black eye could very well be from a bump in the ground or a rock.
From the way Johnny was flipped, he landed on his back; unlikely he could have injured his eye.
Continuity mistake: When Daniel first moves into the apartment, he kicks the outside door open. Then we immediately see Daniel from the inside, and the positions of the pedals on his bike has changed.
Continuity mistake: When Johnny is fighting in the competition at the end of the movie, his hair changes from being clean looking to looking sweaty, back to being clean.
Continuity mistake: During the bathroom scene where Daniel is about to take revenge out on Johnny, watch as Daniel uncoils the hose - it is very long and has several obvious kinks in it. However, as he turns on the water and Johnny runs out, the hose is a perfect straight shot, and MUCH shorter (and water flowing through the hose would not do this).
Continuity mistake: In the scene where Daniel is riding bike home from his mother's work and Johnny and his pals are chasing him on their bikes, they kick Daniel down the hill. As Daniel is rolling down the hill, you can see that it is a stunt double with no cuts on his face and when Daniel re-appears in the shot, his face is bleeding.
Continuity mistake: When Daniel is eating in the restaurant with his mother, from the exterior shot looking in the window, Daniel's hand is underneath his chin. But when it cuts to the inside of the restaurant, his hand is suddenly down near the table.
Continuity mistake: During the skeleton attack by the locked gate, at the bottom of the gate, there are sandbags that disappear and reappear between scenes. Possibly there to stabilize the gate when Johnny flies into it.
Continuity mistake: After the Halloween fight, none of the Cobras injures the next day match what happened to them the night before. Johnny had a black eye although he was only flipped and chopped in the chest. Tommy had his arm in a sling, but he was kicked twice in the stomach.
Continuity mistake: In the final country club scene when Ali is dancing with her father, she glances at Johnny sitting at the table, as her father asks her about how she and Johnny are doing. Then a second later, Johnny is suddenly behind them on the dance floor with Ali's mother.
Continuity mistake: When Mr. Myagi and Daniel go to the dojo to stop the fighting, the earlier scene revealed that they left the apartment at 10am. Assuming that there was some time to get to the dojo, they left a few minutes later and then drove to Mr. Myagi's house to start the training. Daniel starts to wax the cars and the sky is showing a sunset. At the latest, it may have been around 11am when they got to the house, so there is no way the sun could be setting.
Continuity mistake: In the very beginning, when Daniel and his mom start to drive away from their old house in New Jersey, Daniel's bike is strapped to the roof of the station wagon. The bike is positioned with the front tire of the bike facing the back of the vehicle. A couple seconds later, in the very next cut scene, the bike is facing the opposite direction.