Continuity mistake: After Kevin Costner plays the first round of the US Open when he plays horribly, he and his caddie are seen looking at his score being posted on the scoreboard. The number posted for the 18th hole is a 5. Later on, however, when he is talking to Don Johnson in the bar, and Johnson asks him, "How the hell did you shoot an 83?" he replies, "I missed a 5-foot putt on the last hole for an 82." Considering that the announcers say several times that he hit his second shot on number 18 in the water every single day of the tournament, this is impossible. If he hits it in the water, he takes a penalty shot and now he is hitting his fourth shot onto the green, putting for a 5. If he then, as he says, misses the 5 foot putt, he must make a 6 on the hole. I've watched it a thousand times, it just isn't possible.
Other mistake: When Roy makes the bet with Gary McCord on his second shot of the bathroom wall, the bet was he would get the bounce shot onto the green. The ball never gets on the green. The ball is actually on the fringe and a good 5 feet away from the green. Yet Gary still pays the bet that he lost. In reality he won the bet.
Continuity mistake: During the scene where Roy is caddying for Dave Simms, Phil Mickelson hits a shot to the green. Roy says, "He's on the green - in good shape too". However, when Roy's ball lands on the green, Phil's ball is nowhere to be seen.
Factual error: On the final hole, the shot that Roy "has" to make is hit perfectly the first time. For some unknown reason, it spins backward off the green. This is patently impossible with a 3-wood. The club just doesn't allow it, and any golfer on the face of the earth knows it. This scene should have been shot with a long iron, a 2 or 3 iron, which is still very hard to hit, but at least possible (for a pro) to put enough spin to back it up.
Plot hole: In the scene where Roy takes his ball out of the hole, at the last round of the US Open, the crowd are going wild etc. Dave, who has a chance to win the competition, doesn't finish off his round.
Continuity mistake: At the beginning of the movie, Roy has just finished practising and is standing next to his golf bag holding a bottle of beer. He is not wearing a golf glove. However, as he is walking back to the 'clubhouse' he is seen removing a golf glove, with his mouth, from his left hand.
Continuity mistake: During the first competition when Roy is caddying for David Sims we see Roy offer David the 3 Wood. When David refuses they have a discussion. Watch as you see Roy holding the club in his left hand lower the club down holding it in his hand. Right after the discussion we see Roy then once again pull the 3 Wood from the bag and again offer it to David.
Continuity mistake: When Roy is lying on the sofa whilst talking on the phone to his ex-girlfriend, the telephone disappears. At the end of the call he puts the telephone on his chest, but the telephone is not there in the next shot.
Continuity mistake: Nearing the end of the movie, Craig Stadler approaches Molly and asks for a card or two. He has his sunglasses on his head, if you look at his hair, in the first shot its swept down to the side. In the next shot a portion is hanging between the glasses against his forehead. In the following shot as he walks away, his hair is back to sweeping to the side.