Loose Impediments (Rule 23)

You may move a loose impediment (i.e. natural loose objects such as stones, detached leaves and twigs) unless the loose impediment and your ball are in the same hazard. If you remove a loose impediment and this causes your ball to move, the ball must be replaced and (unless your ball was on the putting green) you incur a one-stroke penalty.

 Loose Impediments