Finals of KO, top bracket.
The auction:
P-P-2NT(maybe mis-sorted, maybe state of match)-P-3NT (Puppet was available)-all pass
Opening lead is the spade 10 (Rusinow). Small from dummy. Third hand figures that the oopening is from AJ10x(x) or KJ10x(x). If Declarer has AQ, the 9 would be the right card, giving count. If Declarer has the KQ, thirdhand can catch up later, with Reverse Smith. So, third hand plays the spade 9, to give count.
Declarer counts his tricks before playing. Five hearts, two spades, and a club. He needs the club finesse. If the club finesse works, he has tricks to burn. But, what if the club finesse fails? The opposition will surely cash diamonds for a set. So, what to do???
Declarer then thinks about the defender's problem if he rises with the Ace. his RHO will get in with the club King and lead a spade to his partner's Jack. That person will be mystified and perhaps will think that spade are 5422 with his partner having four to the Queen. This may induce a spade underlead, into the Queen. Maybe not, but it seems like a good hedge. So, Declarer hops the spade Ace. (This, of course, baffles RHO, who suspects 10 from J10xx(x) now.)
Decclarer now starts running hearts. On the second heart, LHO does not want to ditch a club, in case that helps Declarer read the club situation, if that matters. So, he plays a diamond. On the third heart, he's almost forced to ditch a club. On the fourth heart, LHO plops down the diamond King. He figures that this will let his partner know that he has a full five spades, of course expecting his partner to have the Queen. On the fifth heart, LHO ditches another club.
Declarer then hooks the club, losing. His trap is set. RHO dutifully leads the spade, and LHO is in with his Jack.
Put yourself in LHO's situation. From his perspective, Declarer cannot have the hand that he has. Further, winning the first spade high is quite a deep position, if he does strangely have this pattern. But, it seems that his partner, if he had the Queen, should 100% play the Queen and then another spade.
If LHO plays the diamond King now, this could be a disaster. If he leads a small spade, this could be a disaster. If he plays the spade King, the suit might block) if his partner actually holds four spades and did not play the Queen for some reason).
So, LHO decided that Opener had mis-sorted or was weird, cashed the spade Jack, cashed the diamond King, dropping the stiff Jack, and fired a diamond through the 10x on dummy (a diamond was sluffed) into RHO's A9x. Down three.