I think the same about almost all sports movies. For me it's probably that actors have a very hard time duplicating the mechanics of professional athletes. Every time I see an actor swing a golf club, baseball bat, or throw a football or baseball when they are supposed to be portraying a professional I cringe a little.
That said, I still enjoy them enough to watch.
P.S. I think Kevin Costner comes closer to looking natural in baseball or golf than most actors. Can't say the same for Don Johnson or Mat Damon, although I think they are good actors.
Tin Cup is entertaining, but not because it's a great golf movie. It's just entertaining on its own. The Legend of Bagger Vance was disappointing to me, but only because the book is one of my favorites. I didn't think the film lived up to the book, but they never seem to.