Factual error: The movie takes place in 1926 but when the announcer mentions a "Hail Mary" play near the end of the movie the term hadn't been coined yet. Dallas Cowboys quarterback and devout Catholic Roger Staubach was believed to have first used it after executing that play in a 1975 NFL NFC semifinal playoff game.
Continuity mistake: When Dodge shows up for the first practice with Carter, Lexie mentions that it is 8:30. The light and shadows make it appear that it is more like early afternoon. In the next shot, however, everyone's shadows are long on the ground and the light is coming from the side instead of overhead.
Factual error: In the shot of the Chicago Skyline in the final game, you are able to see the Wrigley Building, Tribune Tower, Carbon and Carbide Building, and the Board of Trade Building. All Chicago landmarks of the era, but the field is north, say where Wrigley Field currently is, makes the angle at which you see the other buildings impossible. Also, there are two rather modern (1970s) box-like skyscrapers in the skyline that certainly did not exist in 1925.