The third example where it is correct to ruff in the long-trump hand is the trump coup. A trump coup occurs when the defender can be finessed for a missing trump honour, but declarer does not have enough trump in dummy to carry out the finesse a sufficient number of times. Declarer must shorten his trump to the same length as the defender with the long trump.
The bidding: South opens the bidding with an eleven-count and a good six-card suit. This is a good bid with no wasted points and a long suit. West makes a club overcall, and North shows at least ten high card points with a new suit at the two-level. South rebids his suit showing six and North shows an invitational hand with two-card support. South has a minimum hand and passes.
The Lead: The Ace of clubs.
The play: West plays three rounds of clubs with declarer ruffing the last round. Declarer plays three rounds of diamonds, pitching a spade. He then takes the heart finesse twice with West showing out on the second round. East does not cover an honour with an honour because he can outlast the finesse.
Declarer ruffs the last diamond so that he has the Ace and Queen to East’s King and four. He cashes the Ace of spades and exits a spade. Now the lead for the twelfth trick comes up to his Ace and Queen of trump.
Result: Declarer only loses a spade and two clubs making four hearts for +170.