The line given by John Kruk near the end of the movie, "I'm not looking for athletes, I'm looking for ball players" comes from an interview given by Kruk while playing for the Philadelphia Phillies. In the interview, he stated that he was not an athlete; he was a baseball player.
In order to help the pitcher learn to aim his deadly fastballs better, the kids put a picture of E.J., their nemesis, on the catcher's mitt. If you don't blink you'll notice that the expression on the photo of E.J. changes from "snarling intimidation" to "surprised fear" just before the ball lands in the mitt.
The trivia item below may give away important plot points.
There are three references to Raiders of the Lost Ark (1981) during the scene in Old Mr. Myrtle's house where they discover the baseball. 1) When Tommy takes the ball off the pipe that is holding it, it slowly descends much like the pedestal that held the golden idol just as Indy swiped it. 2) When it begins to descend, Tommy then says, "I've got a bad feeling about this, guys." Echoing a very often said phrase of Han Solo in the Star Wars Franchise. Han Solo of course being played by Harrison Ford who also played Indiana Jones. 3) As Tommy runs away from the traps in the house, a giant baseball rolls down the stairs, similar to the giant boulder that chases Indiana as he makes his escape with the idol.