Continuity mistake: When they start the 18th hole of the last round, the sun is just starting to set (over the Atlantic Ocean, no less). When they get to their tee shots to hit their second shots, it is already pitch black. This could only be a matter of couple of minutes to walk to their next shot. And, yet, at the very end when Will Smith hears the roar of the final shot, he's walking along the beach into the setting sun?
Factual error: When the second round of the tournament is starting and Bagger Vance is telling Rannulph Junuh about 'the field', just after Bobby Jones has taken his tee-shot, Bagger hands Junuh a ball and tee. The tee is a red plastic 'castle' style tee. Apart from being illegal in tournament play, I'm pretty sure they weren't around in the 1920's.
Revealing mistake: During the war flashback there is a newspaper photograph with Captain Junuh on the shoulders of Savannah's young men. When the camera zooms into his face you can see it's someone else's, only in close-up it switches to Matt Damon's. This is surprising because in all other newspaper pictures Matt Damon is nicely worked in.
Plot hole: Junuh gets the lowest score on the 17th hole in the final round, which puts all the players at 'even'. It should therefore have been his honour 18th tee. He actually tees off last, which would indicate that Jones and Hagan had bettered (or at least matched) his score on the 17th.
Continuity mistake: There is a scene when Charlize Theron is talking to Matt Damon while he is sitting in a big stuffed chair. When we see him from the front the top of his head is even with the top of the chair. When we see him from behind, his head is above the chair and his shoulders are even with the top of the chair. The camera angles keep going from front to back and it really looks bad.
Factual error: On the final hole of play, Damon should have placed his ball back to its original position and taken a one stroke penalty. He did not replace the ball to its original penalty, so he would have been deemed to playing the ball from the wrong position, which is another penalty stroke.