I have seen this before. Supporting the plastic would be my guess. Could also prevent the ball from getting stuck between the playfield and the plastic, as the ball would push in the rubber and wedge itself. On a large piece of plastic and on a new flexable plastic, maybe. A peice of felt or one of those white rubber barrels that secures a Gottlieb plastic would make a good cover for the nail.

_{Post edited by Darcy : Clarity.}