Here is an example of passive defense. After a strong notrump opener, a transfer bid and creative interference, declarer receives a trump lead. Right defender plays the Queen. Declarer wins with the Ace and pushes out the King of Clubs. The Ace wins, and flanker plays a second round of hearts, jammer discarding a spade as declarer wins. Declarer plays two winning clubs, discarding spades from dummy, and a low spade. Jammer wins with the nine and plays the fourth club. Declarer ruffs in dummy and tries a small diamond, two, King, Ace. Flanker plays a third round of hearts, defeating the contract.
In this case, flanker sticks to passive defense throughout, never making a play that will blow a trick. The barrage of trump leads prevented declarer from ruffing dummy's fourth diamond, which would have been the ninth trick.