hoist by your own petard

Hurt by your own misdeed. A petard was a medieval bomb made of a container of gunpowder with a fuse, and to blow open gates during sieges against towns and fortresses. Unreliable, petards often exploded prematurely and sent the person who lit the fuse aloft (the “hoist” image) in one or more pieces. The phrase, which is often misquoted as “hoist on one's own petard,” comes from Hamlet: For 'tis the sport to have the engineer Hoist with his own petard; and ‘t shall go hard But I will delve one yard below their mines And blow them at the moon . . .