Continuity mistake: In a bus scene Crash is shown holding a guitar talking about being in the majors. In one scene he's just holding the guitar, the next he has a pair of sunglasses in his hand while holding the guitar. The next scene the sunglasses are gone. A couple of shots later the guitar is sitting in the seat next to him. When Laloosh challenges Crash to a fight, he's holding the guitar again.
Factual error: During Gavin Grey's first NFL game in 1957, the helmets depicted for both the Washington Redskins and Pittsburgh Steelers are historically inaccurate. The Redskins did not employ the burgundy helmets with the feather-stripe running along the center until 1958, and the Steelers didn't use black helmets with the Steelmark logo until 1963. In 1957, the Redskins used solid gold helmets while the Steelers used yellow helmets with a black stripe along the center and black numerals on either side.
Factual error: At the beginning of the film, in the shots of the players in action being voiced over by Comiskey, Cicotte is marking the ball with his fingernail. You can see the modern logo of the sporting goods company "Rawlings" on the ball. It can be seen even more later in the film when Comiskey's assistant is turning a team-autographed ball over in his hands. Rawlings did not start making official major league baseballs until 1976, and even if they had made them in 1919, they very likely did not have the exact same logo. (00:04:30 - 01:28:55)