Mantle throws the ball in from right field, but the second baseman receives the ball as if it comes in from left field.
During Game 1 of the season, announcer Mel Allen says that the Yankees are down 4 runs when Mantle's batting. After he strikes out, the scoreboard on the 2nd deck shows no score.
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.
(At around 20 mins) When Maris meets with the Yankees co-owner, Daniel Topping's cigar smoke is alternately visible and not in between shots.
In the game in Baltimore, the movie shows Wilhelm coming into the 9th inning in mid-inning prior to Maris attempting to hit his 60th home run. In fact, Hoyt Wilhelm started and completed the entire 9th inning; Roger Maris was the 3rd and final batter of the inning.
There was no Sports Illustrated cover with Mickey Mantle and Roger Maris. They were on the cover of Life.
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.
The third deck at the stadium was added digitally in post-production. When Mantle and Maris are taking batting practice near the beginning of the movie, in two shots the ball can be seen to go into the stands and fall through the third deck onto the second.
(At around 32 mins) Anthony Michael Hall's (Whitey Ford) face makeup doesn't match the skin color of his hairline, which is noticeably white.
(At around 19 mins) In the Yankees' dressing room after the 3-2 loss to Cleveland, all the Yankees' uniforms are sparkling clean with no signs of wear or game action.
When Maris is talking with his wife from a payphone after the birth of their son, 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.
When Roger is in the locker room reading through his fan letters, one of the unopened envelopes on the table has a five-digit ZIP code written on it. ZIP codes were not introduced until 1963.
During the 1961 baseball season, stock footage shows a Broadway movie theater playing Mutiny on the Bounty (1962), which was not released until late-1962.
During Maris and his wife's phone conversation, he picks up some Camel cigarettes in a late-1990s pack.
When Mickey Mantle, Roger Maris, and Bob Cerv are watching television, The Andy Griffith Show (1960) opening credits appear in color, but the show didn't air in color until the 1965 season.
When Maris signs the 'X' on the baseball, just outside of Yankee Stadium in Bronx, Detroit's Michigan Central Station can be seen.
In the bar scene, when the other Yankee players were talking to Maris about Mantle's relationship with DiMaggio, Moose Skowron mentions that Joe didn't talk to him at all his rookie year, until the World Series. Moose Skowron did not join the Yankees until 1954, Joe 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 Casey Stengel-managed team), they finished a distant second to the Cleveland Indians who won a then-American League record 111 games.
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.
When Mantle and Maris are playing catch, a reporter tells Maris that Babe 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.
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.