It took Jon a second to realize why he was feeling uncomfortably compressed: Biff was wearing his cup, though Jon had never worn one this uncomfortable, he must still be at football practice. From above Jon and Karyn heard a voice yell, "Ow! What the fuck?" then they felt a hand, presumably Biff's, reach down and shake them about some before grabbing something from between the two of them and retreating leaving Jon and Karyn much more comfortable nestled in the athletic supporter.
"How the fuck did a rock this size get into my cup without me noticing?" the voice from above, obviously Biff, asked no one in particular. "That is so weird. Kind of a pretty rock though, I wonder if Sarah will want it?"
Jon realized that the stone must have come with him when he became one of Biff's balls. Since it had nowhere else to go it had settled into Biff's cup and caused enough discomfort to draw immediate attention to itself.
Even worse than losing the stone it seemed that Biff was going to hand it over to his girlfriend Sarah McMillan. The chances were low that she would discover the stone granted wishes before Jon and Karyn turned back in a week, but just the possibility filled Jon with dread.