Jen_Jen
as pointed out in a previous post
Rule 110 Dead Ball
A ball will be declared dead if any of the following occur, in which case such ball will not count. The pins must be respotted after cause for declaring such dead ball has been removed and the player will be required to re-bowl:
a) If after the player delivers his ball and attention is immediately called to the fact that one or more pins were missing from the setup.
It would be hard to race up to the bowler and tell them before the ball hit the pins that there was one missing. I for one do not look at the pins until after a delivery and I would certainly notice a 5 pin missing, which has happen. I have had to rebowl. but, hey it was my fault for not looking at the pins in the first place. After all are we not playing nine pins are we.