In 1997, baseball commissioner Bud Selig universally retired Jackie Robinson's number, 42. The handful of players still wearing the number were allowed to keep it. As of the film's release, only Mariano Rivera of the New York Yankees continued to wear 42 on a daily basis; Rivera ended his superlative career when the 2013 season concluded, and in 2014 (and barring special requests or approval, all seasons to come) there are no major league players wearing #42.
Pee Wee Reese's line that someday all Dodger players might be wearing the number 42 was actually said by Dodgers outfielder Gene Hermanski in 1951. Brian Helgeland liked the quote so much, he had Reese say it because he is a central character. Since 2004, every April 15th has been "Jackie Robinson Day" in Major League baseball, and every player wears number 42. Robinson's first day in the Major Leagues was April 15, 1947.
In the movie, the punishment for not agreeing to play on the same team with Jackie Robinson was being "traded to Pittsburgh". Branch Rickey left the Dodgers in 1950, and become general Manager of the Pittsburgh Pirates in 1953. Bobby Bragan, who said he wanted to be traded but then asked not to be, ended up managing the Pirates in 1956.
The Birmingham (Alabama) News reported that Birmingham's Rickwood Field, the oldest surviving professional baseball field in the US, "played" three different roles in this movie. It doubled for Franklin D. Roosevelt Stadium in Jersey City, New Jersey, and Forbes Field in Pittsburgh, Pennsylvania, which no longer exist. It also appeared as "itself" in a scene recreating the 1945 season when Jackie Robinson was a member of the Kansas City Monarchs.
When calling the catch of a fly ball in the movie, broadcaster Red Barber says "Back, back, back..." In another play-by-play call, he exclaims "Oh, Doctor!" Contrary to popular belief, Barber didn't use either line regularly. Barber said the only time he used those lines in a broadcast was when he called Al Gionfriddo's dramatic, game-saving catch off of Joe DiMaggio in the 1947 World Series. Since recordings of that Barber call became so famous, many people assumed they were trademark calls.
The movie softens up Leo Durocher's speech to the Dodgers on the eve of their planned strike in protest of the signing of Jackie Robinson. His actual quote was "Don't care if the guy is yellow or black, or if he has stripes like a fucking zebra, I'm manager of this team, he plays!"