Tapping down the line of putt. (Rule 16)
The rule states that a player is not permitted to wipe out, remove, or repair spike marks from the line of putt, which is the line between the ball and the hole. However, the rule permits you to remove foreign objects, such as pebbles, lying on this line, using your hand or the club. The penalty is a loss of hole in match play or a 2 shot penalty in stroke play.