When playing golf in a group, it is important to carry a ball marker so that you can mark your ball on the putting surface. According to the U.S. Golf Association's (USGA) "Rules of Golf," golfers should mark balls with specially made markers, small coins or similar objects. Rule 20 in "Rules of Golf" outlines marker etiquette, lifting, dropping and placing.
When to Mark
When golfers play together, balls on the green should be marked during putting. Golf etiquette calls for the person whose ball is farthest from the hole to putt first, so all other golfers should mark their balls to avoid them becoming an obstruction or distraction to the person putting. The ball should be marked before it is lifted. If the ball is lifted before it is marked, the player incurs a one-stroke penalty. To mark a ball, place the ball marker directly behind the ball and then lift the ball.
If a golfer marks his ball and it is in the line, stance or stroke of another golfer who is putting, the marker may be moved. The marker may be placed one or more club lengths to either side, but not closer to the hole. When the person whose mark has been moved is ready to putt, the marker should be moved back to its original spot.
If a ball marker is accidentally moved in the process of lifting or marking, the marker may be replaced with no penalty. For example, if a golfer fumbles the marker while placing it, no penalty is incurred. However, if the ball moves due to the marker being dropped, then the golfer incurs a one-stroke penalty.
Ball markers should only be placed or picked up by a player or a person whom the player designates to touch the mark. If any player picks up a ball mark without putting down a ball because he believes the hole to have been decided, the player incurs a one-stroke penalty. In addition, if a player moves another golfer's mark, the golfer whose mark was moved does not incur a penalty.
Act of Nature
If a ball marker is moved by forces of nature, such as wind or rain, the marker should be replaced as close to the original spot as possible. The golfer is not penalized.