[inquiry]

This was a disappointing hand in a recent team game event. (Hands rotated so declarer would be south) At both tables ns got to 3nt (other table, where no competition from ew, the auction was 1c-1d-1h-2d-3n-all pass). The opening lead at both tables was the ♠2 with north winning the king. At this table, east won the spade king and incorrectly switched to the heart six (low). What a mistake, but declarer mistakenly won in dummy with the heart ace!!! We are all taught to win with the honor in the short suit hand to avoid blocking the suit, but you shouldn't blindly do that.

Declarer was not punished for his mistake, because although NORTH did the correct thing after that by ducking both the diamond queen and jack, to avoid the diamond suit running, on the next trick, declarer lost a club hook to west, but west returned a heart, giving declarer 2♣ (after he continued clubs), 3♥, 3♦ and 1♠ to make.

The table with the natural auction was equally defective defense. East won the ♠King and correctly returned a spade. WHEN south won the ♠A on the second trick, West made the mistake of failing to unblock the spade suit. Notice, if west throws a high spade honor, the most south can get is 3♦, 1♣, 3♥ and 1♠ before the defense gets in and takes enough tricks to defeat the contract. What I didn't tell you was that North returned the ♠3 (not the ♠4, so South thought North had only 4 ♠ so unblocking might not occur to him.).

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Seeing all four hands, the defense is very clear. But even not seeing all four hands, you should be able to work out what is happening here from both east and west after trick one. Time to consider how the defense should do better.
why would you not want to switch to the heart after spade 2 to he King-Ten?
why would you not want to false card with the original fifth best?
why would you want to unblock spades if partner had five spades?
why might you want to unblock a high spade even if partner had only four spades?
As south, you do see why you should grab the heart with the king, not the ace.

[flametree]

Can you fix the commentary so it agrees with the hands rotated. North keeps popping up with east's cards...

[Antrax]

As south, it's easy. I want to run the diamonds and if they're 4-0 or 3-1 and no singleton K, the defense will win the king on the third round of the suit and then I need the heart ace as an entry.
The heart return must be bad because declarer has to use up the ♥A if he doesn't want my ♦K to win, and then he doesn't have a second entry anyway, so there's no reason to attack his entries. Instead I can clear spades (declarer must have only the A left, since partner promised four and Qx is not a stopper). What I don't understand is why the 3 is a bad return, it seems like the 3 or the 5 are both legitimate.
Unblocking a high spade is good also so declarer can't force us to lead away from our KQ♣, I'm guessing.