Q: Is there a limit to the size of a ball marker that may be used to mark a ball on a green?
A: There is no limit to the size of a ball marker, but the note to Rule 20-1 says a ball ” . . . should be marked by placing a ball-marker, a small coin or similar object, immediately behind the ball.” Note the use of should rather than shall, so there is room for interpretation. However, if a player uses an object that would make replacing the ball in accordance with this Rule difficult or would cause any questions, the player would be penalized one stroke for not complying with Rule 20-1, regardless of where the incident takes place on the course. This would be because the player cannot accurately replace the ball from the spot it was lifted.
Decision 20-1/16 specifically states there is no penalty for using an object that is not similar to a ball marker or small coin, making the note a “recommendation of best practice.” However, this Decision goes on to say that ” . . . it is necessary to physically mark the position of the ball.”
If such a mark could cause a deflection or distraction, a player could request that another object be used for marking a ball.