Never stepped through drywall but I did have similar experience with a block wall at my house. I was getting cocky with my new side grinder/diamond blade combo, cutting in boxes in the bedroom renovation. I would cut it in with the diamond blade and just tap it with my 10lb sledge in a slow pendulum arc.
The chunk would fall out and I had a perfect hole for the box. I got to the last one and when I tapped it nothing happened so I cocked the hammer a few inches farther back. The third time was successful but there was a bright shaft of light coming through the hole. When I bent down to see where the light was coming from I saw my dog, in the yard, with his nose in the hole.
The mason had dropped a little chunk of block in the hole and my "tap" was faithfully transmitted to the outside web of the block. The hole outside was about 8" in diameter.
