When Lou gets his chance to take injured Wally Pipp's place at Comiskey Park, the Yankee dugout is positioned on the first base side of home plate. When Lou returns to Chicago in a later trip with the Yankees at Comiskey Park, he asks Sam Blake about Ellie from the third base dugout.
During the game with the home runs for the boy in the hospital, one shot of the infield shows a dirt path between home plate and the pitcher's mound; all other infield shots show grass in that area.
As Lou is walking up the tunnel after making his speech, the umpire is already saying "Play Ball" yet 15 seconds earlier the field was totally crowded with dignitaries.
When a young Lou hits the baseball over the fence and breaks the store window, the police officer and store owner come running onto the field before Lou even gets to second base. This would be an impossible reaction time for anyone to respond with the breaking of the window just merely seconds beforehand.
The home run that Babe Ruth promised and hit for the little boy in the
hospital is said to have gone to center field. When the ball was hit, its trajectory is towards right field. The play-by-play announcer said it went to center field. There is no way the ball could have gone to center field.
Lou Gehrig played his first game as a Yankee during the 1923 season. Yet, when he enters the Yankee clubhouse for the first time (looking at the lockers, trying on his hat), the lockers of Mark Koenig and Bill Dickey are shown. Koenig joined the Yankees in 1925, and Dickey in 1928.
When Lou enters the Yankees' clubhouse in 1923, he sees Tony Lazzeri's name on one of the lockers. Tony did not join the Yankees until 1926.
The film shows Lou meeting Eleanor Twitchell on a road trip to Chicago during his rookie season (1923). In reality, the pair first met at a party in 1932.
The movie shows Gehrig's consecutive games streak ended when he took himself out of the lineup in the fifth inning. In reality, Gehrig had approached manager Joe McCarthy in the hotel that morning with his decision. Either way, Gehrig benching himself in the middle of a game would not have stopped the streak, as baseball rules say a player who completes one half-inning in the field or one plate appearance is credited with having played in the game (so his streak would not have ended until the next day).
As Gehrig (Cooper) is doing his homework at Columbia, he writes with his right hand. Whilst Gehrig batted and threw left-handed, like many lefties of the era (perhaps because of "correction" in school), he wrote with his right hand.
After the wedding in Gehrig's apartment, the crowd of workers and family waves goodbye to Lou and Eleanor. As the couple leaves, the worker sitting on a ladder painting the white wood beam raises his hand to wave goodbye. The man shoves his hand into the ceiling of the set, pushing the apparently solid ceiling inward, exposing the ceiling as nothing but fabric.
When Eleanor (Teresa Wright) pulls up to the kids' ball game that Lou (Gary Cooper) is umping, there is no windshield in the car.
When young Lou Gehrig hits the home run that breaks the glass, the pitcher never throws the ball. It shows the pitchers arm coming through, then cuts to the behind shot and his arm is coming forward again. But he never releases a ball. Her swings and the ball appears in the lower left hand corner of the frame, then magically goes through the building and breaks the window.
Young Lou's sandlot hit came from an empty pitcher's pitch. The actual "hit" ball appears to be shot out of a device (perhaps a pitching machine) beneath the bottom left of the screen. There's an initial white blur and then the trajectory of a ball that starts well above and to the left of the bat and goes at a "southwest to northeast" angle not possible from the bat.
In the movie, Lou Gehrig hits two home runs and Babe Ruth hits one for "Little Billy" in the hospital. According to baseball-reference.com, in the 1928 World Series Gehrig did not hit multiple home runs in any game that Ruth did homer. In game 3 against the St. Louis Cardinals, Gehrig hit 2 home runs and Ruth none. In Game 4 Gehrig hit one and Ruth three. Whilst the movie is not specific about the game being in the 1926 or 1928 World Series where both the Yanees and Cardinals met, there are two ways to tell it is 1928. One, Gehrig did not homer in the '26 series. Two, the Yankees are celebrating a series victory later in the movie. The Yankees won the '28 series and lost in '26.
When Lou and Eleanor are introduced at the Chicago restaurant, a house band is heard playing "I'll See You in My Dreams" in the background. The song was not published until 1924, a year after Gehrig's rookie debut (when the scene takes place).
When Walter Brennan gets stopped by two motorcycle cops whilst driving Lou and his wife to the ballpark just after their 1933 marriage, a 1941 Buick business coupe (as a police car) is shown. A subsequent shot on a thoroughfare shows various 1940-41 cars.
When Lou hits the first of his two HRs during the 1928 World Series, the shadows of two light towers can be seen on the field. Lights were not installed at Major League ballparks until the late 1930s.
The Yankees played 2 World Series against the Cardinals while Lou Gehrig was on the team, in 1926 and 1928. Whichever World Series the movie was depicting (assuming 1928, the one where Gehrig hit 2 home runs in one game), Gehrig's #4 is clearly visible in those scenes, but the Yankees' uniforms did not have numbers on their backs until 1929.
In the World Series game Gehrig hits 2 homers, it's in St.Louis, however, the crowd reactions are not consistent with when they should be cheering and when they shouldn't be.
During the collage of Gehrig's first road trip as a starter, when the Yankees are in Washington, a runner is shown running from 1st base and sliding into home, under the catcher's tag. (It's known that they flipped the film to make Gary Cooper, a right hander, look like he was left handed, like Lou Gehrig.)
This is not a "Revealing mistake" as knowing "they flipped the film" is not the same as seeing the mistake on the film. Also, according to a Trivia item, the only "flipped" footage was a brief sequence portraying Gehrig's minor-league days at Hartford. Instances of Cooper throwing a ball as a Yankee were filmed using his stand-in, Babe Herman.
This is not a "Revealing mistake" as knowing "they flipped the film" is not the same as seeing the mistake on the film. Also, according to a Trivia item, the only "flipped" footage was a brief sequence portraying Gehrig's minor-league days at Hartford. Instances of Cooper throwing a ball as a Yankee were filmed using his stand-in, Babe Herman.
In the opening scene, set during or shortly after Babe Ruth's 1915 rookie season, young Lou Gehrig offers an older boy a Grover Cleveland Alexander baseball card, but the older boy calls Alexander an "old timer"; at the time, Alexander was 28, and early in his prime as the National League's top pitcher.