A ruffing finesse occurs when declarer holds a sequence in one hand and a void in the other. In this layout, South is on lead with spades as trumps:
Dummy
T987
--
43
--
West
East
--
--
K65
432
AKQ
JT9
--
--
South
A
QJT
65
--
South has two natural diamond losers, but can shed them by leading the Q toward dummy.
If West covers with the K, then dummy ruffs. South comes back to hand with the A and discards dummy's diamonds on the JT.
If West ducks the Q instead, declarer throws a diamond from dummy and leads another heart, thereby repeating the ruffing finesse.
Example
Dummy
Q
KJ962
K963
432
South
JT94
AQT875
--
AQ5
West
1
3
All Pass
North
Pass
4
East
2
Pass
South
3
6
Figuring dummy for a spade singleton or void on the auction, South optimistically barrels into 6. West's opening lead is the 3, won by East's ace. At trick two, East returns the J.
South knows that East should have played the K (the lower of two touching honors) if holding both the ace and king. South can also count 22 HCP between his hand and dummy, and East has just advertised 5 HCP. Therefore, West should hold both the K and K to justify an opening bid.
South, then, should spurn the club finesse and try a ruffing finesse in spades. At trick two, he wins the A and proceeds to draw trumps, finding them 1-1.
South now leads the J through West for a ruffing finesse. If West covers, then dummy ruffs and South returns to his hand via a trump to play spade winners, dumping club losers from dummy. If West ducks the J, then South pitches a club from dummy and continues with the T. Either way, South's losing clubs can be ruffed in dummy to make the contract. The full deal:
North
Q
KJ962
West
K963
East
K8732
432
A65
4
3
AQ54
South
JT872
K76
JT94
JT98
AQT875
--
AQ5
See also
Backward Finesse
A finesse that's taken in the "opposite" direction of a regular finesse.
Chinese Finesse
The lead of an unsupported honor as a pretense to a legitimate finesse.
Coup En Passant
A trump trick scored by ruffing a card "behind" a defender who holds a higher trump.
Crossruff
A strategy of ruffing losers back and forth between declarer's hand and dummy.
Double Finesse
A finesse against two opposing honor cards.
Dummy Reversal
A strategy in which declarer's long trumps are used for ruffing losers, and dummy's short trumps are used for drawing the opponents' trumps.
Intra-Finesse
A type of finesse against three opposing honor cards.
Marked Finesse
A finesse made obvious by the auction or play of the hand.
Obligatory Finesse
A type of ducking play that finesses an opposing honor.
Ruff and Sluff
A play in which declarer ruffs a card in one hand while discarding a loser from the other.
Simple Finesse
A finesse for a card (usually an honor) held by the opponents.
Triple Finesse
A finesse against three opposing honor cards.
Two-Way Finesse
A card combination in which either defender can be finessed for a queen.