Continuity mistake: Toward the end of the movie when the Dragons are facing the Giants for the Pennant, Hammer is up to bat and get a hit. When you see him round first base, they show a picture of the dugout, where you will find him holding a large hammer. It's tough to be at bat and on the bench.
Other mistake: Towards the end of the movie when the Dragons are playing the Giants for the pennant, Uchiyama argues with the umpire when he called Jack out for touching home plate. He bumps him not once, but twice. No umpire would stand for this; Uchiyama would've been ejected from the game immediatley.
Other mistake: At the end of the film, Hammer agrees to join the Los Angeles Dodgers just in time for a weekend series against the Atlanta Braves. The problem here is that the Dragons won the Central League Pennant and thus, qualify for the Japan Series. The Dragons wouldn't allow him to leave until the postseason has been completed.