Wrong Ball

Question
In stroke play, I understand that if someone hits the wrong ball then he incurs a two stroke penalty, but if the player whose ball was hit then accidentally hits that player's ball that hit the wrong ball then does he also incur a penalty?

Answer
Yes he does as he too hit the wrong ball.  However, if the format was match play, the first to hit the wrong ball would lose the hole.

15-3. Wrong Ball
a. Match Play
If a player makes a stroke at a wrong ball, he loses the hole.

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.

If the player and opponent exchange balls during the play of a hole, the first to make a stroke at a wrong ballloses the hole; when this cannot be determined, the hole must be played out with the balls exchanged.

Exception: There is no penalty if a player makes a stroke at a wrong ball that is moving in water in a water hazard. Any strokes made at a wrong ball moving in water in a water hazard do not count in the player抯 score. The player must correct his mistake by playing the correct ball or by proceeding under the Rules.

(Placing and Replacing ?see Rule 20-3)

b. Stroke Play
If a competitor makes a stroke or strokes at a wrong ball, he incurs a penalty of two strokes.

The competitor must correct his mistake by playing the correct ball or by proceeding under the Rules. If he fails to correct his mistake before making a stroke on the next teeing ground or, in the case of the last hole of the round, fails to declare his intention to correct his mistake before leaving the putting green, he is disqualified.

Strokes made by a competitor with a wrong ball do not count in his score. 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.

Exception: There is no penalty if a competitor makes a stroke at a wrong ball that is moving in water in a water hazard. Any strokes made at a wrong ball moving in water in a water hazard do not count in the competitor抯 score.

Thanks for the question and I'm sorry for the delay in answering; I was in Bermuda playing golf.

Fairways and Greens,

John