Revealing mistake: When Howard is reading the book about how to "score with babes" his lines are on a piece of paper on the page. You can see this by the different color papers. (00:46:25)
Revealing mistake: Towards the end of the film when the Yankees are trying to close out Game 6 of the World Series you can tell the "real" footage they use is not from the World Series. They are playing the Atlanta Braves in the World Series but you can see the Baltimore Orioles logo on the field in a number of shots.