2019 Rule: Rule 13.1c(2) allows repair of almost any damage on the green:
“Damage on the putting green” will be defined to include all types of damage (such as ball-marks, shoe damage, indentations from a club or flagstick, animal damage, etc.), except aeration holes, natural surface imperfections or natural wear of the hole.
Reasons for Change:
Because putting greens are specially prepared for playing the ball along the ground, the Rules allow the player to do things on the green that are not allowed anywhere else:
The player may mark, lift and clean a ball on the green at any time, remove sand and loose soil on the green and repair old hole plugs and ball-marks on the green.
Given this philosophy of allowing players to try to have a smooth surface for rolling the ball, there is no conceptual reason for prohibiting repair of other types of damage (whether made by players, animals, maintenance staff, etc.).
This Rule change will eliminate the frequent questions among players and referees about whether a particular area of damage on the green is a ball-mark that may be repaired or is a shoe mark or other damage that must not be repaired.