Factual error: Joe Jackson batted left-handed in real life, not right-handed as Ray Liotta portrayed. He also threw right-handed and not left-handed like it shows when Kevin Costner is hitting him fly balls to left field.
Factual error: When he bats, Jake uses a helmet with no earflap. In 1983, it was instituted that players must wear a helmet with at least one flap; however, it's possible that Jake is exempt from this rule under Major League Baseball's "grandfather clause," which allows any player who played before 1983 to continue using the flapless helmet. (01:34:40)
Factual error: The storyline in Karate Kid 3, based on the happenings and reference points of the first two movies, is supposed to take place roughly about late 1984, or early 1985. However, if you look close at the beginning of the film when Terry Silver drops off John Kreese at the airport, there are several cars that are definitely later 80's models.