When the twins are playing at Fenway Park, they are in the first base dugout, which can be seen when the camera is facing Billy and you can see Pesky Pole in the background. The Red Sox's home dugout is actually on the first base side, and the visitors' is on the third base side
When Ken Griffey Jr dives back to first base on the pickoff attempt his uniform is dirty and he brushes himself off. However, when he makes the leaping catch against the wall to end the game, his uniform is perfectly clean.
In the last inning of the game between the Twins and the Mariners, Dave Magadan gets his uniform dirty after being tagged out sliding into second base, yet in the bottom of that inning he makes a diving catch and stands on his knees and you can see his uniform is clean. This is similar to the Ken Griffey Jr. incident as well.
When the players are dropping the water balloons out the hotel window a bucket is seen containing more water balloons. When it cuts back to the shot with the bucket, the bucket is empty. The next cut shows that the water balloons are back.
After Billy inherits the Minnesota Twins, it is referenced that he also inherited the stadium. However, this is incorrect, as the Metrodome is not owned by the Twins or any other sports team, but the Metropolitan Sports Commission, the governing body of professional sports and interests in the Twin Cities.
At the beginning of the film when Billy's three teammates are on third base, the umpire calls everyone out and then is corrected by Billy. However, none of the runners were tagged by the defense so at that time, no one was out. The runner who was standing on the base could have run back to second base and the batter-runner could have run back to first base (touching second) on the way. In essence, all three runners could have been safe at the end of the play if they had returned to other bases.
The Metrodome was also used for Football by the University of Minnesota and the NFL's Minnesota Vikings. As a result, the outline of a football field could be seen on the baseball field during late and post-season games played by the Twins. However, no outlines of the football field are seen on the field for the Twins season ending series in the film.
When Billy names himself manager this would not be allowed by the league. Major League Baseball rules prohibits managers and players from owning shares of their teams unless approved by the commissioner. This rule was enforced on May 11, 1977 when Atlanta Braves owner Ted Turner suspended the current manager, Dave Bristol, and took over as manager for one game. With Billy's extensive baseball knowledge he should have known this and it would have been stopped by the league if he tried to take over. However, Billy receives approval of the commissioner (and his mother) that allows him to manage the team.
"During the final game when the Twins are playing the Mariners for the Wild card spot, Bowers attempts to pick off Ken Griffey Jr. using the team's trick play. How ever this play would be illegal. You can NOT fake a pick off throw to first base." True while on the rubber. If the pitcher steps behind the rubber before the fake, it is legal. The camera angle on Bowers' fake does not show his feet on the play. Miami ran this play in the 1982 College World Series, nicknamed the Grand Illusion.
In the last inning against the Mariners, Mickey Scales grounds out to second and they show Dave Magadan playing first base. Then Pat Corning lines out to third base which was played by Dave Magadan. Then Larry Hilbert singles to the outfield and when they show him on first base once again Dave Magadan is playing there.