During the season opener the announcer mentions that hitter Billy Brubaker has been struggling with the wood bats this season. Obviously he would not know this nor is it possible since this is the season opener.
When Ryan's buddies are keeping track of the number of strikeouts that he gets in the last game by posting the 'K' signs they mistakenly post the Ks backwards when batters swing at the third strike. The backwards K is the baseball scorekeeping symbol for a strikeout in which the batter does not swing at the third strike. (Though this might be excused as character error).
At the end of the movie when the credits are being shown on the scoreboard the current Phillies lineup is listed. Outfielder Bobby Abreu's name is spelled Bobby Abreau. In the DVD/Home release, his name has been corrected
Near the beginning of the movie, the brief shot of the light stanchion clicking on (to illuminate the field for a night game) is actually a reversal of the actual footage. This was done for effect as mercury-vapor lights (commonly used in such applications) take some 4-7 minutes to achieve full brightness after being switched on. Now, they do (almost) go completely dark when turned off (with a faint glow lasting for a short while). If you view this closely, you'll notice that the lights are glowing at first and then snap up to full bright.
When Miles catches the fly ball that causes him to leap over the outfield wall, this is recorded as an out. This is correct. The result of the play is an out, not a home run. MLB rule 7.04(c) states, "If a fielder, after having made a legal catch, should fall into a stand or among spectators or into the dugout or any other out-of-play area while in possession of the ball after making a legal catch, or fall while in the dugout after making a legal catch, the ball is dead and each runner shall advance one base, without liability to be put out, from his last legally touched base at the time the fielder fell into, or in, such out-of-play area."
At a couple of points in the movie, characters are shown reading Internet news articles about the baseball season. In both cases close inspection shows that the URL of the pages begins with "file:///", meaning that the page is not online but on the local computer.