It is an obstruction if both the ball and the obstruction are on the putting green you get free relief for line of play.
16.1 Abnormal Course Conditions (Including Immovable Obstructions)
This Rule covers free relief that is allowed ...............
a. When Relief Is Allowed
(1) Meaning of Interference by Abnormal Course Condition. Interference exists when any one of these is true:
• The player’s ball touches or is in or on an abnormal course condition,
• An abnormal course condition physically interferes with the player’s area of intended stance or area of intended swing, or
• Only when the ball is on the putting green, an abnormal course condition on or off the putting green intervenes on the line of play.
