Continuity mistake: At Happy's first tournament (the one he goes to with Chubbs), when Chubbs does the 'it's all in the hips' motion there is a lake behind him and Happy. However, when Happy then hits his ball and we see the overhead shot from the ball's point of view, we can see that there's no lake anywhere near them - it's just a green fairway.
Continuity mistake: In the scene where Shooter is with the other pro golfers, (the ones with the gold jackets) and they're drinking wine, Happy interrupts them wearing an ACDC top. Notice Shooter's wine glass switch hands a number of times, and when he tells Happy to meet them on the 9th green, the wine glass has disappeared totally.
Continuity mistake: On the last hole, Shooter McGavin overshoots the hole and the ball ends up going past the green. However once he shoots the ball off the man's foot and onto the green, we now see him coming onto the green from the fairway side at the bottom of the screen, not from behind the green past the hole.