This deal was played in a 2022 world-championship qualifying event. East held:

K3
AJ32
K742
986.

LHO opened 1 and after RHO showed clubs, opener showed a flat hand and landed in 4. Partner leads the 7 (an "obvious" singleton) and you see:

	J86 4 A95 AKJ1042	YOU
		K3 AJ32 K742 986

Declarer wins dummy' A and leads a spade to the queen which wins. This doesn't look good; in fact it looks like 12 easy tricks.

But declarer, an expert, next plays a low spade to dummy's jack. Surprise--you are in with your K. Now what? Hint: Don't worry about overtricks; this is team scoring and your goal is to set the contract.

Why is declarer playing this way? He is likely missing K10xxx and this was a safety play to guard against your holding K10xx (he didn't want to lay down the A and see your partner show out).

So, you have a spade trick and can give partner a club ruff. Then you get your A...for only 3 defensive tricks. This was the Real Deal:

Vul:None Dlr: South	J86 4 A95 AKJ1042
1072 Q8765 Q863 7		K3 AJ32 K742 986
	AQ964 K109 J10 Q53

At trick 4, East made the brilliant play of a low heart. Sure, declarer could have put up the K and drawn trump for 12 tricks. But declarer (a well-known expert) didn't know where the A was. He was afraid the K would lose to the ace. Another heart would make dummy ruff. Declarer would have no way back to his hand to draw the last trump. Stuck in dummy, he would have to play a club (ruffed and then a defensive heart trick).

Declarer guessed that LHO had the A. Accordingly, he played the 10 on the heart return. West won and if he ad the A, all would be good for declarer. The most declarer could lose was a spade, heart and a club ruff.

But, West didn't have the A. He won the Q and returned a heart. Now, declarer was dead. He discarded from dummy (not that ruffing would be any better). East won and now issued the club ruff for down 1. Nice defense.

Still, I think declarer's safety play was too safe. True, the layout he ran into was unlucky, but laying down the A was unlikely to cost. Declarer was catering to West having started with two black singletons (not very likely).