Balls often get stuck behind the Sanctum drop target on The Shadow. During the ball search, the drop target goes down, the ball rolls over it, then the drop target is fired upwards, causing the ball to hit the glass at a perpendicular angle, and quite hard. This has not chipped or fractured, never mind shattered, the glass on my game. I can't imagine too many airballs hitting the glass with as much force (anything off the flippers will hit at quite a shallow angle), so I don't think there's any danger of genuine pinball glass shattering. If ordinary glass has been used to replace the original glass however...