Continuity mistake: In the beginning of the movie he is not taken onto the hockey team. After he is hustling at the driving range he goes to toughen up. As he is toughening up, Chubbs unplugs the machine. The kid tries it, but he never plugged it back in and the machine still manages to work. (00:15:10)
Suggested correction: The kid plugged it in off-camera.
Trivia: During one of the tournaments, a few of Happy's fans are visible in the background holding cut out signs of his face. This is the same but blown up picture used in Billy Madison to mark the grade he was in.
Suggested correction: I Googled the face sign from this movie while watching Billy Madison, and they are not the same. You can tell the facial expression on Happy Gilmore features a wider smile and arched eyebrows, whereas the cutout of Billy Madison is more straightfaced and his eyebrows are a little furrowed, as evidenced by the wrinkles between them.
Continuity mistake: After Happy gets hit by the car he's lying on the ground and you can see he's only wearing the Subway shirt. But when he tees off near the end he's wearing a shirt over the subway one.
Suggested correction: He's wearing the orange button-down shirt the whole time.
Other mistake: When Bob Barker reaches up to grab Happy by the neck, his head is resting on the grass immediately before and after that shot. Happy was standing fully upright, so there's no way Bob Barker's arm could have been that long.
Suggested correction: Happy isn't standing. He's kneeling. You can see him stand after Bob grabs him.
