Left and Right are overlapped, sailing downwind and fighting for position.  The wind is coming over the port quarter of both boats and their booms are off to starboard; i.e. they are on port tack.  Left is windward boat and is struggling to stay clear of Right (see quiz #1).  Left moves their boom over to port and claims right of way as a starboard tack vessel under Rule 10  (port/starboard rule).   Right must respond by:
 
A. Giving way to Left.  She has been out-smarted and has no other choice.
B. Ignoring Left.  Left is “sailing by the lee” and is therefore still on port tack and is windward vessel.
C. Immediately shifting her boom onto port side in order to recover the right of way.
 

See the answer below:

 The answer here will be easy if we can determine if Left has truly become a vessel on starboard tack by moving her boom to the opposite side of the boat even though the wind angle has not changed and she is sailing by the lee.   Lets look at the definition of port and starboard tack:

Tack, Starboard or Port -- A boat is on the tack, starboard or port, corresponding to her windward side.
This will only be helpful if we can determine which is the windward and leeward side:

Leeward and Windward -- A boat’s leeward side is the side that is or, when she is head to wind, was away from the wind. However, when sailing by the lee or directly downwind, her leeward side is the side on which her mainsail lies. The other side is her windward side. When two boats on the same tack overlap, the one on the leeward side of the other is the leeward boat. The other is the windward boat.

It is clear that the determining factor for leeward/windward and port/starboard is the position of the boom.  Sailing by the lee is of no consequence.

 The correct answer is A.  Left has gained the advantage, although they need to keep their heads down in the case of an accidental gybe!  Note that it will be of little use for Right to follow suit and shift their boom to port since they will then be windward vessel and must continue to give way to Left.

 Consider why this rule makes sense.  Winds can shift rapidly and may be different for boats that are relatively close together.  How would you objectively determine if a boat was sailing by the lee at a given moment in time?  The position of the boom is always clear.
 

 If you have a rules situation that you'd like to see covered in the quizzes, send an e-mail to mast_yc@geocities.com  There's a wealth of information on the racing rules at Art Engel's site http://www.racingrules.org/   including a rules guide and some additional quizzes. A current rules book is included as part of membership in U.S. Sailing – check for membership information at  http://www.ussailing.org   The rules are posted on the International Sailing Federation Web site at http://www.sailing.org