Footage from a game in Toronto, Canada between the Yankees and the Blue Jays on 1 October 2004 was shot for the movie. Drew Barrymore and Jimmy Fallon were present at the game and she threw out the first pitch.
Erin Nanstad and Dan Cummings are actual, die-hard Red Sox fans who appeared in Still We Believe: The Boston Red Sox Movie (2004), a documentary about the Red Sox's heartbreaking 2003 season. Dan appears in Fever Pitch as a Fenway Park vendor in the 1980s and Erin as a fan.
During game 4 of the ALCS, the stadium announcer can be heard to introduce John Olerud. However in reality Olerud injured his foot in the previous game and missed the remainder of the series.
Right before the scene where Lindsay gets hit with the ball, the legend on the screen says it's July. The ball Miguel Tejada of the Orioles hits into the stands, which hits Lindsay, is thrown by Mike Myers of the Red Sox. Mike Myers wasn't picked up by the Red Sox until August 6, 2004.