All fouls must be called and acknowledged before next shot is taken. (exception: scratching)
The following results in fouls:
a) A ball being pocketed, or;
b) The cue ball contacting a cushion, or;
c) The frozen ball being caused to contact a cushion attached to a separate rail, or;
d) Another object ball being caused to contact a cushion with which it was not already in contact.
Failure to satisfy one of those four requirements is a foul.
A ball which is touching a cushion at the start of a shot and then is forced into a cushion attached to the same rail is not considered to have been driven to that cushion unless it leaves the cushion, contacts another ball, and then contacts the cushion again. An object ball is not considered frozen to a cushion unless it is examined and announced as such by either the referee or one of the players prior to that object ball being involved in a shot.