The instant that the Referee has determined that a shot is over, time will be started. Any subsequent ball falling, no matter how close to time starting, will be treated as falling without being hit, and it shall be replaced where it was prior to falling. Only the fallen ball will be replaced even if other balls were moving. 

Exception, if it is absolutely clear a moving ball would have struck the ball that fell, the fallen ball is replaced also all other balls are restored to the positions before the shot was played. The same player will then play again without penalty. The Player may decide to play a different shot. 

If a ball falls in without being hit timing shall be restarted when the ball(s) have been replaced.