North led the King of Clubs.    North-South Vulnerable.

In a matchpoint club game, West opened with a Gambling Three Notrump, showing a long solid club or diamond suit with no ace or king outside. Our aggressive East was prepared with a conventional defense, the Ripstra Convention. As played here, this convention called for bidding four of your better minor to show the majors, pinpointing the opposing minor in the process. East passed, and South, with the best hand at the table, made a slam try with a bid of five hearts, asking in this situation for North to bid slam with 2nd round control of the opposing suit. So despite his rock bottom minimum, North bid slam.
 
West began the defense with two top clubs. Declarer trumped the second lead with Dummy's Ten of Hearts, holding plenty of trump winners and knowing from the auction that East was out of clubs. South counted 11 top tricks by way one club ruff, 5 hearts in hand, 2 high spades and 3 high diamonds. He still needed to develop one more trick for slam.
 
When declarer ruffed the second club high, East was for a brief moment on the spot. A diamond discard would unguard that suit and allow North to later cash 4 diamond tricks. And throwing a spade would be no better! East knew from the bidding that South held both the ace and king of spades, and that a spade discard would allow South to pull trump, cash spade ace and king, enter Dummy in diamonds and ruff a spade, bringing down the suit and making Dummy's 13th spade high.
 
Having eliminated his options, East found his only safe play by discarding a trump on dummy's ten of hearts - an underruff. None of his trumps were destined to win a trick, and playing one now left South with no winning option. South tried to apply pressure by cashing all five hearts, but on the last two, East was discarding after Dummy, and was able to maintain length parity with Dummy, protecting the 4th round of both pointed suits.  Down one!
 

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