Injured by the device that you intended to use to injure others.
The phrase ‘hoist with one’s own petard’ is often cited as ‘hoist by one’s own petard’. In the USA, ‘hoisted’ is preferred so the alternative forms there are ‘hoisted with one’s own petard’ is often cited as ‘hoisted by one’s own petard’.All the variants mean the same thing, although the ‘with’ form is strictly a more accurate version of the original source.

Hoisted with your own petardA petard is, or rather was, as they have long since fallen out of use, a small engine of war used to blow breaches in gates or walls. They were originally metallic and bell-shaped but later cubical wooden boxes. Whatever the shape, the significant feature was that they were full of gunpowder – basically what we would now call a bomb.

The device was used by the military forces of all the major European fighting nations by the 16th century. In French and English – petar or petard, and in Spanish and Italian – petardo.

The dictionary maker John Florio defined them like this in 1598:

“Petardo – a squib or petard of gun powder vsed to burst vp gates or doores with.”