Character mistake: In the opening scene with the mobsters threatening and then beating up Mr. Stillwell, the American flag in his dojo is hanged backwards, with the blue Union on the right. (00:04:20)
Character mistake: Jason's dad comes out of the car and uses consistently for the first part of the movie his crutch supporting the side where he has the cast. Walking on just one crutch, you have to support the uninjured side. (00:08:55)