I was using a cup wire wheel in a hand grinder to clean up a water outlet clamped in my vice. In order to go around the sides I gripped the side handle back handed as in the picture, allowing me to turn it sideways as I went.
The wheel caught the side of the outlet, and this was the result.
the white spot in the center is where it apparently cauterized some of it from the friction heat.
I keep a first aid kit, plus alcohol, and hydrogen peroxide in the shop, so I washed it with the peroxide, then put some burn ointment on and then bandaged. So far the pain is not as bad as I expected.
The problem was that the way I was holding the front grip put me in a position I could not control the kickback. I had never realized till then that a wrist does not have near as much strength preventing movement toward the outside, or toward the little finger, however you want to look at it, as it does going the other way. Apparently you do not have the reflexes to stop in from going in that direction either.