Continuity mistake: When Molly comes for her first golf lesson, Costner takes the last bite of his hot dog. In the next scene, he still has some of the hotdog left.
Roy is up by a stroke or 2 on the final hole of the US Open, until he decides to go for the green instead of laying up. The drive does land right near the cup, but rolls down the bank and goes into the water. Instead of taking a drop where it went into the water, he hits from the same spot and puts it in the drink again. He does this at least four or five times. Facing disqualification for running out of balls, he hits another shot from the same location, but this time it lands right near the cup and drops in. Roy ends up with a 12 on the final hole, but he does qualify for the Open the next year, and ends up with Rene Russo.
Happy Gilmore
More mistakes in Tin Cup
Romeo Posar: Now THAT was a defining moment. And the definition was "shit."
Trivia: Kevin Costner made most of his own golf shots in this film.