Other mistake: Josh's birthday, according to the milk carton, is in the winter. But, some time after he celebrates his birthday at the Italian restaurant, he returns to his childhood neighborhood and it's fall (colored leaves, etc.). It can't be the following year because he's only gone for a total of a few weeks.
Other mistake: When Josh and Billy are over the balcony dropping the water balloon on the mover on the street, the balloon is shown dropping from an overhead angle off course from hitting the man below, yet we hear him scream being hit, when it easily would have missed him where Josh dropped it.
Answer: Paul (John Heard) tells Josh that the serve has to cross the yellow line. When Josh calls the ball short, Paul is basically trying to cheat and claims he never said the ball has to cross the line. Although I'm trying to figure out what racquet sport their playing. It looks like they're playing on a handball court, but the racquet sports I know, the ball has to cross the short line (the yellow line in "Big") on the serve but you also serve from a service area where you have to stand in front of the short line, which they don't do.
Bishop73