How should you play this hand to make the maximum number of club tricks? South was dealing, with no one vulnerable:

                        NORTH
                       ♠️ 10 2
                       ♥️ 9 7 5
                       ♦️ 7 4 2
                       ♣️ A Q 6 4 3

WEST                                        EAST
♠️ Q 8 7 5 4                             ♠️ J 9 6
♥️ 8                                          ♥️ K Q J 3 2
♦️ K Q 10 8 5                          ♦️ J 9 6
♣️ K 8                                     ♣️ J 2

                      SOUTH
                     ♠️ A K 3
                     ♥️ A 10 6 4
                     ♦️ A 3
                     ♣️ 10 9 7 5

The bidding proceeded as follows:

South         West         North          East
1NT           All Pass
Opening lead: ♦️K
In a duplicate game a declarer at one table won the opening lead with the ♦️A and then did what seemed natural: led the ♣️5 to the ♣️Q. The ♣️A dropped the ♣️K and ♣️J: oh, happy day! But when South continued the suit with the ♣️3, the suit was blocked. The ♣️10 and ♣️9 won tricks, but the ♣️4 languished on the board.

Another declarer led the ♣️10 to the ♣️Q and then dropped the ♣️9 under the ♣️A. By unblocking, South created five club tricks. The ♣️3 was led to the ♣️7 and the ♣️5 was overtaken by the ♣️6, creating an avenue for the ♣️4 to win the fifth club trick. South won nine tricks in all for a 91.7 percent result.

The Official Encyclopedia of Bridge defines unblocking as “throwing a high card in play to gain some advantage for the hand opposite.” The entry provides this example, with no side entry to dummy in a NoTrump contract:

             A 10 6 2
J 9 8 3               K 7 5
             Q 4

When the 3 is led to the king, declarer must unblock the queen. By subsequently finessing the 10, two tricks are available. If the queen isn’t unblocked, it will take the only trick in the suit.
Similarly, the defense can unblock, as per another NT entry:

                  A 3 2
Q 10 6 5 4              K 7
                  J 9 8

When the 5 is led and captured by the ace, East must unblock the king. Once in lead, East plays the 7 to the 10, and the defenders pick up four tricks in the suit.

Unblocking is an extremely important aspect of the game. Unless players have the foresight to unblock (jettison) high cards to establish lower ones as entries, lines of communication between opposing hands can sometimes be easily severed. Unblocking keeps these lines of communication open as a means of facilitating play both on offense and on defense.