TRY out this challenge to your defensive skills. South opens the bidding with one notrump (15-17 points) and is raised to three notrump by his partner. East-West do not enter the auction. West leads the 7 of spades and this dummy appears:
' 9 5
'* A 6 4
'¶ K J 8 7
'£ Q J 10 6
You are East, holding:
' J 6 4 3 2
'* Q J 9 3
'¶ 10 5 4
The 9 of spades is played from dummy at trick one. How do you plan the defence?
Obviously, you should begin with an analysis of the opening lead. It appears that, most likely, the 7 of spades is a fourth-highest, in which case you can be certain that South holds precisely two spades. It seems that since you have only four points, partner will hold at least one entry card, and accordingly there are realistic prospects that the defence my be able to run the spade suit, thereby defeating the contract.
But did you notice the problem? You are the one with the long card in spades, and if you play your jack of spades at trick one, you will no longer have a card in spades high enough to take over the lead from your partner in order to cash the fifth spade -- the presumed setting trick.
Could it help to play a low card, or could that instead cost a trick? It is true that you would lose a trick if partner has led from the king-queen of spades and declarer started play with the bare ace-10. But if that unfortunately is the case, the suit would have been blocked anyway, and you would never score your fifth spade.
All things considered, best play must be to signal with your 6 of spades at trick one. Declarer's hand:
' K Q
'* K 8 5
'¶ A 9 2
'£ A 9 7 4 3
Declarer cannot capture nine tricks without finessing in clubs, whereupon your partner, after winning the king, will be able to cash the ace and 10 of spades, then you will overtake his 8 of spades with your carefully-preserved jack and your last spade will suffice to set the contract a trick.