When a person is playing anywhere in the infield in softball and misjudges how to play the ball (or if they just suck). The ball then bounces or takes a "bad hop" and hits the player in the face often causing a broken nose or black eye. The threads of the ball also leave a mark or bruising making it look like a softball stamp.
Skip had no business playing softball but he played first base anyway. Spence hit a hard ground ball in Skip's direction and it softball stamped him. Skip realized he was too old to play and never played again.