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.
Continuity mistake: When the Rad Pack first meets and are skiing together, Dan O'Callahan is wearing a blue baseball cap and sunglasses. In some later shots he is wearing a stocking cap and goggles. (00:31:25 - 00:32:00)
Continuity mistake: When Roy breaks his bat in the playoff game, the bat is a long way from the batter's box; the "Wonderboy" fragment is lying further away from the foul line than the rest of the bat, and the fragment "point" faces away from the foul line, the top of the bat on both parts face the line. However, in the close-up, the fragment is facing the other way, with the point facing the foul line. Note, too, that when Hobbs hits the ball, the bat is not split. (02:09:10)