A Grand Coup is a play in which declarer ruffs one or more winners to intentionally shorten his trump length. From Ely Culbertson's "Contract Bridge Complete":
"When one winning card is ruffed, it is a Single Grand Coup; ruffing two winning cards makes a Double Grand Coup, etc. In the following example of the Grand Coup, declarer shortens his trump length by two cards, each time ruffing a card which would otherwise be a winner:
| | North | | |
|  Q9 | |
|  AKQJ | |
| West |  KJT | East |
| 8 |  8543 | K754 |
| 87432 | | T96 |
| 9743 | South | 862 |
| AK6 | AJT632 | Q72 |
| 5 | |
| AQ5 | |
| JT9 | |
South
1
2
4
|
|
West
Pass
Pass
All Pass
|
|
North
2
2NT
|
|
East
Pass
Pass
|
"West opens the club King, and East-West take three club tricks. East returns a heart, won by dummy's Jack. Now the Queen and nine of spades are finessed, both winning. The heart Queen is led from dummy and South ruffs it. A small diamond puts dummy in with the ten, and South ruffs the King of hearts.
"Next the diamond Queen is led and overtaken by North's King. Now dummy leads the heart Ace. If East ruffs, South can overruff; therefore East discards his last diamond and South discards the diamond Ace. When dummy now leads a diamond, East must ruff and South overruffs, winning the last two tricks and making four spades."
