"18-1 - By Outside Agency
If a ball at rest is moved by an outside agency, there is no penalty and the ball must be replaced.
Note: It is a question of fact whether a ball has been moved by an outside agency. In order to apply this Rule, it must be known or virtually certain that an outside agency has moved the ball. In the absence of such knowledge or certainty, the player must play the ball as it lies or, if the ball is not found, proceed under Rule 27-1.
(Player’s ball at rest moved by another ball – see Rule 18-5)
*PENALTY FOR BREACH OF RULE:
Match play – Loss of hole; Stroke play – Two strokes.
*If a player who is required to replace a ball fails to do so, or if he makes a stroke at a ball substituted under Rule 18 when such substitution is not permitted, he incurs the general penalty for breach of Rule 18, but there is no additional penalty under this Rule."
I think that this answers your question, Roger.
