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Explain the defense suit combination

#1 User is offline   Trumpace 

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Posted 2006-February-01, 12:21

Yesterday, I was kibitizing a teams matchs between experts and world class.

This was one situation.



Spades were trump.
Declarer is south, who had opened 1S sometime (showing 5 or more spades)
Declarer needs all spade tricks to make the contract.

Declarer led the ♠Q and the west (a world class player) played low without a flicker!

Can you explain why/why not is this a good play? (assume Apriori odds, i.e no other information about other suits is known).
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#2 User is offline   kenrexford 

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Posted 2006-February-01, 13:31

One possible explanation (there are a few) is to cater to QJ8 in Declarer's hand. If you cover the King, Declarer is forced to take a winning finesse against partner's 10. If, however, you duck, Declarer may be 50-50 as to whether to drop your doubleton King or to smother your partner's doubleton 10.

In a slam, ducking might be right when Declarer might need one of two finesses to work but cannot guess wrong. Declarer would then try the Queen at dummy on the one, planning to rise unless covered. If covered, the guess is gone. If ducked, Declarer rises and tries the other guess.
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#3 Guest_Jlall_*

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Posted 2006-February-01, 13:36

If declarer has QJ8xx, ducking will put him to a guess (one that he will likely get wrong). A mixed strategy IS correct here as if you only cover with KT doubleton declarer will pick it off, but usually one should duck with Kx in this situation. If partner has T8x declarer will lead the jack next anyways and not take your losing option (especially when partner drops the 8 under the Q :)) If declarer has QTxxxx we made a big "oops." In fact I once made a slam with the trump suit of QT9xx opp A9xx by leading the queen and a very very good lho ducking (not knowing i had 5).
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#4 User is offline   MickyB 

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Posted 2006-February-01, 13:44

You don't *have* to use a mixed strategy - the important thing is to not cover more than one-third of the time. If you do so, it starts being right for declarer to finesse on the way back. If you cover precisely one-third of the time, the finesse and the drop are equal probability.
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#5 User is offline   Trumpace 

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Posted 2006-February-01, 14:41

MickyB, on Feb 1 2006, 02:44 PM, said:

You don't *have* to use a mixed strategy - the important thing is to not cover more than one-third of the time. If you do so, it starts being right for declarer to finesse on the way back. If you cover precisely one-third of the time, the finesse and the drop are equal probability.

Deciding to cover not more than one third of the time, _is_ mixed strategy, isn't it? :)
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#6 User is offline   MickyB 

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Posted 2006-February-01, 14:45

Trumpace, on Feb 1 2006, 08:41 PM, said:

MickyB, on Feb 1 2006, 02:44 PM, said:

You don't *have* to use a mixed strategy - the important thing is to not cover more than one-third of the time. If you do so, it starts being right for declarer to finesse on the way back. If you cover precisely one-third of the time, the finesse and the drop are equal probability.

Deciding to cover not more than one third of the time, _is_ mixed strategy, isn't it? :)

Only if you cover more often than never ;)
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