It happens more than you think. I have several that sometimes do the same thing on certain shots if they are hit just right. I've never known one to even chip the glass let alone break it. My other suggestion is to play the machine lower down in front of it and not in your open robe so your balls stay well under the top of it

I agree with Robin... you can never be too high

Actually I never even thought about the placement of the flipper rubbers. As they don't have a specific slot to fit in that is a very good point and tip he makes. Usually the shots I get that hit the glass are the ones that come off the flippers to a certain spot. Most likely they have lofted the ball from hitting the upper edge of the flipper rubber.

Ok .. I just dropped the thread down another level with that first comment .. my bad.