Opponent hits wrong ball

Question
A friend of mine and I were playing a cheap 9 hole course today and we ran into a ruling question I couldnt really answer.  His second shot goes down the middle of the fairway about 140 from the pin.  His third shot is over and right of the pin under some trees, a very poor spot to be with an elevated green.  As he is walking up the fairway he sees HIS ball, which meant the ball he had just played was not his ball.  So he thinks all he has to do is just play his ball and ignore the shot he just took, with no penalty.  I explain to him there should be some kind of penalty, because he essentially got two shots from only ten yards apart, all because the first ball he hit wasnt his.  I believe this was an accident on his part, but because of the accident he got two shots at it, and sure enough, his second shot is 5 feet from the pin.  He sinks the put and he thinks he won the hole fair and square, because he mistakenly hit a wrong ball.  A very fortunate mistake indeed.  

We were playing for two dollars a hole, nothing really, but I couldnt let it go.  Especially considering he really thought it was fair.  If I had to guess, or say whats fair, then he should just play his first shot as if it was his ball and go from there, replacing the wrong ball with his.  PGA rules are somewhat vague about this so any help you might have would be great.  

Thanks, Matt  

Answer
Hello Matt.  You are right, your opponent occurs a two stroke penalty in stroke play and loses the hole in match play.  The fact you were playing for $2/hole indicates match play.  Here is the rule quoted verbatim from the rules of golf which can be found at www.usga.org.

"a. Match Play
If a player makes a stroke at a wrong ball that is not in a hazard, he loses the hole.
There is no penalty if a player makes a stroke at a wrong ball in a hazard. Any strokes made at a wrong ball in a hazard do not count in the player抯 score.
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 ball that is not in a hazard, loses the hole; when this cannot be determined, the hole must be played out with the balls exchanged.
b. Stroke Play
If a competitor makes a stroke or Strokes at a wrong ball that is not in a hazard, he incurs a penalty of two strokes.
There is no penalty if a competitor makes a stroke at a wrong ball in a hazard. Any Strokes made at a wrong ball in a hazard do not count in the competitor抯 score.
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."

The rules can be hard to understand at times but this one is pretty clear and the player is responsible for playing the correct ball which should have markings on it.  Players in USGA or PGA events usually announce on the first tee what brand, number and markings they will be playing that round.

So, Matt, go collect the two dollars and tell your friend he's lucky it wasn't for a great deal more.

Fairways and Greens,

John Brott
www.golfnutts.com