Because there was no accurate documentation of it, no one knew what the precise color of the Yankee Stadium seats were in 1961. When faced with this dilemma, production designer Rusty Smith was told that Billy Crystal had an old bleacher seat from Yankee Stadium. Though the seat was completely painted blue, Smith found one small chip of green on the seat that proved to be the true Yankee Stadium green.

Most of the details of the games recreated for the film were based on Billy Crystal's firsthand memories of having seen or watched the actual games. As a result, the film's crew members nicknamed him "Rain Man" (from Rain Man (1988)) for his uncanny ability to remember the games to the smallest detail.

Despite the way Mrs. Ruth (Claire Merritt Hodgson) is portrayed in the film, she actually visited Roger Maris after his 60th home run. Maris whispered in her ear, "Don't feel badly; no one will replace The Babe."

The part of Baltimore Oriole knuckleball pitcher Hoyt Wilhelm was played by real-life major league knuckleball pitcher Tom Candiotti.

As a close friend of Mickey Mantle and his family, Billy Crystal was given permission by the family to honestly portray Mantle's drinking and carousing. Many of the moments in the movie of Mantle getting drunk really happened. This includes his getting drunk and calling home at 2 a.m. from his hotel room, as in the scene following the death threats to Roger Maris and his family.

Billy Crystal: he lends his voice several times in the film: 1: The director yelling "Cut!" when Roger Maris and Mickey Mantle try to film a commercial; 2: The Detroit Tigers' 3rd base coach yelling, "Hold Up! Hold Up!"; 3: The TV announcer for Maris and Mantle's commercial. Crystal also appears as a fan in the stands when Mantle gets a standing ovation as he starts batting practice on Opening Day. He can be seen in the upper deck crowd in the front, wearing a navy blue shirt.