Quoted from boilerman:gottlieb experimented on a hand full of games and produced them with particle board pf's. big hit is one of them. what you are seeing is the particle board swelling from moisture. the damage is done, nothing can be done to reverse it,
The white paint in the flipper area where you usually see a clear wood finish indicates particle board instead of plywood.
Volley is another game where some of the pf's are particle board with the white paint.