Blonde tennis joke

While out one morning in the park, a jogger found a brand new tennisball, and seeing no one around it might belong to, he slipped it intothe pocket of his shorts.
Later, on his way home, he stopped at the pedestrian crossing,waiting for the lights to change.
A blonde girl standing next to him eyed the large bulge in his shorts."What's that?" she asked, her eyes gleaming with lust.
"Tennis ball," came the breathless reply.
"Oh," said the blonde sympathetically, "that must be painful.... Ihad tennis elbow once."