"Unblocking" is the play of an unusually high card to a trick. The purpose is to maintain communication between declarer and dummy.
| | Dummy | | |
|  AKQ43 | |
| West | | East |
| J95 | | T |
| South | |
| 8762 | |
In this layout, South is on lead and needs all 5 tricks. Assuming that there are no additional entries to dummy, South must play the 8-7-6 on the first three rounds of spades. If South starts out by leading the 2 to dummy, he will be forced to win the fourth round of spades in his own hand, thereby blocking the suit.
An unblocking play may also be necessary when the defense is on lead:
| | Dummy | | |
| 52 | |
|  AT2 | |
| West |  — | East |
| K7 |  — | Q63 |
| J73 | | K8 |
| — | South | — |
| — | A94 | — |
| Q5 | |
| — | |
| — | |
In this five-card ending, West leads the 3 to East's king. If South unblocks the Q, he can win East's spade return and then finesse in hearts for two tricks.
Example
| | Dummy | | |
| 7432 | |
| 6 | |
| West | AT9 | East |
| QT8 | KQJT9 | K9 |
| 75 | | QJT9 |
| K875 | South | Q632 |
| 8763 | AJ65 | A54 |
| AK8432 | |
| J4 | |
| 2 | |
South declares 3NT. West leads the 5 (understandable, but not ideal for the defense). After East plays the Q, South can count 8 tricks: 4 clubs, 1 diamond, 2 hearts, and 1 spade. The 9th may come from a diamond finesse if South unblocks at trick one.
Accordingly, South plays the J beneath East's Q. When East returns the Q, South wins and then leads a club to knock out East's ace. Now South can win any return and finesse in diamonds to make the contract.
