This Real Deal was reported to me by my most fertile source, David Berkowitz. It was played in an online expert team game. Vulnerable against not, South held:

AQ75

K9875

--

A1085.

In 3rd seat, he opened 1. LHO overcalled 2 and partner made a negative double. After a competitive auction, East-West sacrificed against 4 in 5. South went on to 5 and received the 6 lead:

	KJ96 42 3 KJ9732
	AQ75 K9875 -- A1083

One of my students (Sally) never seems to make a plan. As soon as dummy comes down, she says: "Thank you, Play Low." Whether you say thank you or not, that's not a good way to play bridge. The expert declarer took a look at dummy and played low. He won the queen with the ace and started to draw trump. Had they been 3-2, you wouldn't be reading about this deal. The Real Deal was:

Vul:N-S Dlr: North	KJ96 42 3 KJ9732
3 A63 AQ98764 64		10842 QJ10 KJ1052 Q
	AQ75 K9875 -- A1083

As you can see, declarer couldn't handle it. If he draws all the trump, he gets only the 10 top tricks. If he attempts to trump dummy's diamond in hand, he can't get back and forth.

Because you can claim if spades are 3-2 (draw trump, run clubs and ruff a diamond), you need to plan for 4-1 spades. Four with West would be okay (you could take two high ones, trump a diamond high and then take a marked finesse against 10xxx if needed). But the actual layout would spell doom.

How to prevent it? Play High, Sally. The 6 lead is hardly going to be from Q64. When you win dummy's K, the clubs will still run. But now you have easy communications. You ruff a diamond at trick 2 and draw trump and claim.

It turns out, that this misplay didn't cost too much. The other tables (IMP-pairs) were all in 5X making East-West.