I have moved this question over from an unrelated Outside Agency Post.  The question comes from Don in Buffalo, Minnesota.

QUESTION:

YOU ARE PLAYING MATCH PLAY/ YOU HIT YOUR BALL
INTO THE ROUGH. YOUR OPPONENT FINDS YOUR BALL,
PICKS IT UP AND DRIVES AWAY ON HIS CART.

WHAT PENALTY DOES HE RECEIVE?

Don,

You question has many parts and depends on how your ball was moved.

Generally, in Match Play, if your opponent moves your ball in play and it is not during search, the opponent incurs a one stroke penalty and the ball must be replaced.  The player is not penalized.  If the ball is moved by your opponent during search there is no penalty to either player and the ball must be replaced.  This is Rule 18-3.

If you knew the exact location of the ball or the lie of the ball, it may be replaced.  If these are not know (e.g. your opponent ran over your ball with a cart) the ball must be dropped as near as possible to where it came to rest but not nearer the hole.  The drop is often required because if you didn’t know the lie or location of the ball, the Rules, in fairness, require you to take your chance with how it came to rest - this is accomplished by dropping the ball.

If the opponent drove off some distance and the ball it is not immediately recoverable (in a few seconds) you are permitted to substitute another ball without penalty.  The ball must be substituted in the same manner above, based on your knowledge of the original exact location or lie of the ball.

Thank you for your interest in the Rules of Golf - regards,