Occasional Item #3 Laws of the Game

Running Jack or Bowl:

6.1	A bowl played while the jack or preceding bowl is in motion shall be forfeited.
6.2	If a running jack or bowl appears to be in danger of striking a still bowl or jack belonging to another end, such running jack or bowl should be stopped and returned to be replayed.

Still Jack or Bowl:

7.4	If the jack or any bowl is displaced by the jack or a bowl of any other players, or by any exterior cause, and the players agree as to the spot of replacement, the end must be continued, otherwise the end is void.