If a player substitutes a ball when not entitled to do so they incur a penalty of two strokes in stroke play, or loss of hole in match play, for a breach of Rule 15-2, part of which states;
If a player substitutes a ball when not permitted to do so under the Rules (including an unintentional substitution when a wrong ball is dropped or placed by the player), that substituted ball is not a wrong ball; it becomes the ball in play.
If the mistake is not corrected as provided in Rule 20-6 and the player makes a stroke at an incorrectly substituted ball, he loses the hole in match play or incurs a penalty of two strokes in stroke play under the applicable Rule and, in stroke play, must play out the hole with the substituted ball.
Of course, players may change balls at will between the play of two holes (unless there is a One Ball Condition of Competition), as they do not have a ball in play at that time.
Two examples of when a player unintentionally substitutes a ball are;
- When a ball is marked and lifted from the putting green, put in a pocket and then a different ball is replaced at the marker and played. This precludes a player from having a favourite ball for putting only.
- When a ball is lifted from a putting green and is accidentally dropped or thrown somewhere from where it cannot be retrieved, e.g. in deep water of a water hazard.
An example of when a player intentionally substitutes a ball when not entitled to do so is;
- When a player notices that they are playing the same brand and number of ball as another player in their group and they change their ball, so as to easily distinguish between them, Decision 15/6.5.
However, there are several instances where a player is not penalised for substituting a ball, as Rule 15-2 also states;
A player may substitute a ball when proceeding under a Rule that permits the player to play, drop or place another ball in completing the play of a hole. The substituted ball becomes the ball in play.
Examples of where the Rules permit substituting a ball are;
- When taking relief from a water hazard, Rule 26-1.
- When playing under penalty of stroke and distance, Rule 27-1, even if the original ball is not lost or out of bounds.
- When the player deems their ball unplayable under Rule 28, whether or not the original ball has been retrieved.
- When a ball has come to rest in a place that is dangerous to the player (e.g near a poisonous snake or a bees’ nest) and they are permitted to drop a ball away from the danger, Decision 1-4/10.
- When it has been determined that a ball has become unfit for play, Rule 5-3.
- When a ball has been lifted under the Rules, due to suspension of play, the player may replace the original ball, or a substituted ball, Rule 6-8.
- When a ball to be dropped or placed is not immediately recoverable by a player after they have caused it to move; e.g. if it was accidentally kicked into water; because it is in or on a movable obstruction, Rule 24-1, or an immovable obstruction, Rule 24-2; because it is in an abnormal ground condition, Rule 25-1.
Note that there is no penalty is a player lifts a ball that has been incorrectly substituted and replaces it with the original ball, provided they have not made a stroke at it. Rule 20-6 states.
A ball incorrectly substituted, dropped or placed in a wrong place or otherwise not in accordance with the Rules but not played may be lifted, without penalty, and the player must then proceed correctly.