Rule 15: Wrong and Substituted Balls

From the USGA's Official Rules of Golf

White golf balls with one yellow one.
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The United States Golfers Association (USGA) dictates the way the professional sport is meant to be played in its online rulebook "The Official Rules of Golf," whose Rule 15 dictates how wrong balls and substituted balls are to be handled during professional and recreational gameplay.

Although it may seem obvious, a player is expected to keep up with and play off of the same ball from tee-off to sinking it in the hole, but there are certain guidelines for when a ball can be replaced or substituted in certain situations, especially when the ball is lost or out of bounds.

Rule 15-1 lays out the general rules associated with golf balls in play while 15-2 governs the use of substituted balls and 15-3 governs what happens when a wrong ball is played or continued to be played off of in both stroke and match play.

General Play and Substituted Balls

According to Rule 15-1, "A player must hole out with the ball played from the teeing ground, unless the ball is lost or out of bounds or the player substitutes another ball, whether or not substitution is permitted, which is governed by Rule 15-2, which states that a player can substitute a ball when another Rule permits the player to play, drop, or place another ball, wherein the substituted ball becomes the ball in play.

Rule 15-2 also provides an important distinction for a substituted ball over a wrong ball by saying that "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."

However, Rule 20-6 provides a correction for the mistake, which if not taken 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."

One exception to this is that if a player incurs a penalty for making a stroke from a wrong place, there is no additional penalty for substituting a ball when not permitted, which is dictated in  Rule 20-7.

Wrong Balls in Match and Stroke Play

In match play, a player loses the hole if he makes a stroke at the wrong ball, and if the wrong ball belongs to another player, its owner must place a ball on the spot from which the wrong ball was first played.

Rule 15-3 states that in match play, "If the player and opponent exchange balls during the play of a hole, the first to make a stroke at a wrong ball lose the hole; when this cannot be determined, the hole must be played out with the balls exchanged."

During stroke play, though, a competitor incurs a two-stroke penalty if he makes a stroke at a wrong ball and must correct his mistake by playing the correct ball, and if he fails to correct this mistake before the next hole, he is disqualified from the competition.

Rule 15-3.b states that "Strokes made by a competitor with a wrong ball do not count in his score" and "If the wrong ball belongs to another competitor, its owner must place a ball on the spot from which the wrong ball was first played."

One exception to both of these rules is that there isn't a penalty if this occurs while in a water hazard, wherein the ball is moving in the water.