Anachronisms: When Maris is talking to Mrs. Maris on the phone, we see a modular phone jack (not in use until the '70s).
Factual errors: Bob Cerv was not a member of the Yankees in the beginning of the 1961 season, he was a member of the Los Angeles Angels.
Continuity: Mantle throws the ball in from right field, but the second baseman receives the ball as if it comes in from left field.
Anachronisms: Seats in Detroit have cushions with the modern Tigers logo, not installed until the early 1990s.
Anachronisms: During Roger Maris and his wife's phone conversation, Roger picks up some Camel cigarettes in a pack that wasn't designed until the late-90's.
Revealing mistakes: The third deck at the stadium was added digitally in post-production. When Mantle and Maris are doing batting practice near the beginning of the movie, in two shots you see the ball go into the stands, and fall through the third deck onto the second.
Continuity: After the commissioner's decision to make separate records for the 162-game season, Maris is answering questions while playing catch. When he stops to talk to the reporter (clearly breaking from playing catch), he had just thrown the ball to his partner. When he's done talking, he immediately throws the ball again to his partner, though he never received it during his break.
Anachronisms: When Mantle, Maris, and Cerv are watching television, the opening credits of "The Andy Griffith Show" appear in color, but the show didn't air color episodes until the 1965 season.
Factual errors: In the bar scene, when the other Yankee players were talking to Roger about Mickey's relationship with Joe Dimaggio, Moose Skowron mentions that Joe didn't talk to him at all his rookie year, until the World Series. Skowron did not join the Yankees until 1954, Dimaggio retired after the 1951 season, therefore, the two were never teammates. Plus, the Yankees did not even make the World Series in 1954. Even though the team won 103 games (the most for a Stengel-managed team), they finished a distant second to the Cleveland Indians who won a then-American League record 111 games.
Factual errors: Detroit Tiger Pitcher Frank Lary was right handed, not left handed as depicted in the movie.
Factual errors: Maris hit #53 off of Hank Aguirre, not Frank Lary. He hit #52 off of Lary.
Factual errors: Maris hit #58 off of Terry Fox, not Jim Bunning.
Factual errors: Maris and Mantle hit his respective 45th homer on the same day: Mantle in the 1st game of a double-header, Maris in the 2nd. In the movie, Maris hits his 45th and Mantle his 44th.
Factual errors: A reference is made to President Kennedy interrupting a news conference to mention that Maris has hit #47 and #48. Kennedy did not hold a news conference that week in August, nor ever mention Maris during one. President Kennedy would never interrupt a press conference, let alone interrupt one to praise the accomplishments of Yankees' player. He was too big a fan of the Boston Red Sox for that.
Factual errors: There was no Sports Illustrated cover with Mantle and Maris. They were on the cover of Life.
Factual errors: The broadcast of the opening day game describes the Twins pitcher as "Pascual" - a reference to longtime pitcher Camilo Pascual. He did not pitch that day - Pedro Ramos pitched a complete game for the Twins.
Anachronisms: When Roger is talking with his wife from a payphone after the birth of their son, Randy, he's talking on a payphone that is a single-slot model. In 1961, the three slot version (25 cent, 10 cent 5 cent) was still in use. The single-slot phone was not introduced until 1965.
Factual errors: When Mantle and Maris are playing catch, a reporter tells Maris that Ruth hit .343 the year he hit 60 home runs in 1927. Ruth actually hit .356 that year, and never hit .343 during any of his 22 seasons.
Factual errors: Many players refer to Mickey Mantle as being 18 years old when he was a rookie. He was actually 19 years old in his rookie season, 1951.
Anachronisms: During a scene set during the 1961 baseball season, stock footage shows a Broadway movie theater playing Mutiny on the Bounty (1962) -- not released until late 1962.
Factual errors: In the game in Baltimore, the movie shows Hoyt Wilhem coming into the 9th inning in mid-inning prior to Maris attempting to hit his 60th home run. In actuality, Wilhelm started and completed the entire 9th inning; Maris was the 3rd and final batter of the inning.