is it justified to shoot someone that is stomping on someone else's head?

in my state, yes. you should, however, warn the stomper to cease before firing

Not legally.

However the state may choose not to prosecute.

You can at least fire the gun in the air or put in his face to get his attention.

most places allow you to prevent the death of another and that can include shooting the attacker.

if you drew on them and told them to stop a few times and they didn't I doubt you'd get into trouble. but I didn't even warn them, you'd could end up behind bars.

The person is in danger of loosing their life.

I would say taking shot is justified.

No it is considered self defense if you feel threatened and you are protecting someone from being killed. Fire at will