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.
Trivia: The film is based on the real-life events of the 1919 Black Sox scandal, in which members of the Chicago White Sox were charged with "throwing" the World Series (i.e. losing on purpose). Even though many people believe he wasn't involved, "Shoeless" Joe Jackson was banned from baseball and hasn't been inducted into the Baseball Hall of Fame because of that.