Continuity mistake: We first see from the inside of the door (and therefore backwards) the instructions that Mr. Miyagi leaves for Daniel to paint the house. In the next shot we see the same note from the outside - from Daniel's viewpoint. Clearly they are two different notes. The left & right arrows switch directions, the drawings of the hands change, the position of Miyagi's signature changes, and the placement of some of the exclamation points changes.
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Other mistake: In the semi-final where John Lawrence fights against Darryl Vidal, the female referee has major problems of what to do. When Lawrence gets his first point, the referee first raises her red flag (Vidal is wearing the red ribbon) but then swiftly changes her mind. And when Lawrence gets his third point, the female referee again incorrectly raises her red flag.
Continuity mistake: After Daniel's little party at Miyagi's, they both go outside and Daniel sits in the yellow car and Miyagi walks up. In the shot from the front Miyagi has his hands crossed leaning on the car door, yet from the back he has his elbow leaning on the door, then back to just his hands on the door.
Continuity mistake: Before the dance in Mr. Miyagi's work area you can see the red shower curtain with the polka-dots that Danny wears to the dance hanging on the wall. After the dance, when Danny is in the work area after getting saved from the Skeletons, you can still see the shower curtain on the back wall.
Continuity mistake: In the scene where Mr. Miyagi teaches Daniel defensive moves, Daniel blocks Mr. Miyagi's punches with his right hand on the 'paint the fence' move. Daniel then leaves his right hand high, in a defensive position. This shot is taken behind Daniel, over his left shoulder. The next shot, a side view with Daniel on the right of the screen, shows Daniel's left hand held higher, as if he'd used that hand all along.
Deliberate mistake: During the final match, Johnny scores his second point with a forearm to Daniel's side. However it is incorrectly announced as a kick to the side. Johnny was on one knee at the time and in no position to kick him. Also, you can see Johnny throw a forearm and not a kick.