According to the US Golf Association, a player can borrow a ball from another player as long as it's the same brand and model, so if Roy hit his last ball into the water, he may or may not have been disqualified, as Romeo stated.
During the opening credits and the opening scene, the range is shown at twilight, and Roy hits balls into the setting sun, yet when he and his entourage enter the pro shop, the light coming through the blinds, as well as the view of the range through the front door clearly show it to be daytime. When Roy and Molly step outside to begin her first lesson, it is twilight again.
When teeing off on the 18th hole during the final round Turk can be seen in the crowd behind the tee box. Later, during the play of the same hole, he is in the bleachers alongside the 18th green. An incredible sprint for a 300 pound man.
David Simms tells Roy and Romeo that the purse for his tournament is half a million dollars. When Gary McCord and Phil Mickelson are making bets with Craig Stadler, the announcer says it's a $250,000 purse.
CBS golf producer Lance Barrow offers that Salome is in West Texas near Floydada. Floydada is in the panhandle about 60 miles east of Lubbock, not near Fort Stockton as the road signs at the first of the movie suggest. Barrow is from Floydada and was probably giving a shout out to folks back home.
In the bar after the first round, Roy commented that he didn't shoot an 82 because he missed a four footer on the 18th. The scoreboard showed that Roy shot 5 (par) on the 18th to shoot 83. Yet, following Roy's shot into the water on the 18th in the third round, broadcaster Jim Nantz stated that he had found the water for the third straight day. If Roy had put the ball in the water with his second shot on the 18th in the first round and missed a four footer on that green the best score he could have had would have been a 6. (Drive + shot into water + penalty stroke + approach shot + missed putt + made putt = 6)
In the bar following the first round of the US Open, the Brickyard 400 NASCAR race is on the TVs. This race is held the first weekend of August every year; the US Open is always in June. Also, the first round is played on Thursday, not the weekend.
On the last hole of the Open when Roy finally puts the ball in the cup and then proceeds to toss it into the water, several guys trample across the green and dive in the pond to retrieve the ball and one hoists it up once found. There is no way they would have been able to distinguish that ball from the other balls he hit into the drink. Not to mention they would have been tackled by security as Roy's playing partner still needed to complete his hole.