Board-a-match scoring may account for the aggressive bidding here: The difference between -140 and -50 could decide the fate of the board. North-South were using a three-way Polish club system: One club could be natural, a weak notrump or very strong. West showed 15-18, and South’s three hearts showed 18 or more with a primary heart suit. When East stretched to balance with four clubs, South’s four-diamond call was not an underbid facing a known near-Yarborough.
Against four hearts, West, New Zealand international Matthew Brown, kicked off with two top clubs, ruffed by declarer with the heart queen. When declarer advanced the spade king, Brown assumed South had five diamonds (given the bidding) and only five hearts (based on that play of the heart queen). The goal was to score a diamond trick in addition to a spade, a heart and a club, but declarer was threatening to set up dummy’s spades for three discards.
Brown found a counter by ducking the spade king! Declarer was stuck now. If he continued spades, West could win and return a spade for East to ruff away one of dummy’s tricks. If, instead, declarer played the heart ace and another heart to draw East’s trumps, West would win the second trump trick and return a third trump to kill the dummy.
Winning the first spade is fatal for the defense. The best West can do is return a third club. Declarer ruffs in hand and plays the spade queen, followed by the heart ace and another heart. Ducking the spade trick is the only way for West to keep control.