Here was an interesting defensive problem a pair of experts had against me in the Sunday Swiss in Greenville last week. I'm glad they got it wrong.

Dealer: S Vul: NS	North ♠ A93 ♥ A64 ♦ Q5 ♣ K9863
		East ♠ 752 ♥ K872 ♦ K6 ♣ AT74

South	West	North	East
1♠	Pass	2♣	Pass
2NT	Pass	4♠	Pass
Pass	Pass

Defending against 4♠ at imps, you are east and your partner leads the ♥J. You win the K. What now? What inferences can we make about the hand so far?

For lack of anything better to do at this point and no current danger of your diamonds going away, you return another heart. Declarer wins in hand and then plays the ♣J, partner contributing the 2.  What’s going on now? What hasn’t declarer drawn trumps yet? You duck the club to try to get a better idea of what is happening before you have to make another decision, but declarer continues with the ♣Q, partner following with the 5. This time you take the ace. What do you lead now? Why?

Declarer obviously isn’t worried about getting overruffed in clubs but he was sure in a hurry to set up the club suit. Could partner be able to trump a heart? No, that would give declarer 4 hearts and he surely would have bid 2♥ instead of 2NT. Partner and declarer are out of clubs but can it be right to try to give partner a trump promotion by leading another club? Let’s construct a few possible hands for declarer. There are just enough outstanding high cards for partner to have the ♦A.

♠KJTxx ♥Qxx ♦Axx ♣QJ. If declarer has this hand (or pretty much any hand with the ♦A), the contract is unbeatable. Leading a club might help partner score the Q but that won’t be enough to defeat the contract.

♠KQJTx ♥Qxx ♦Jxx ♣QJ. If declarer has this hand, you must cash diamonds now or at least one of them will go away on clubs. Of course, leading a diamond risks giving up an overtrick when declarer has the first hand. At imps you need to play the ♦K to have any chance at defeating the contract. At matchpoints this is a much more difficult play to make, as holding them to 4 may well be the best you can do while letting them make 5 would be worth almost no matchpoints.