How severe does an injury have to...?

it really does depend.....at one point my dad had a card that he had to carry due to his training that basically meant his hands where considered a deadly weapon..........in the main IF you can deliver those types of blows then you SHOULD have the training and self control to pull back at the last moment and not break or kill anyone but certainly put them on their butt and make them pay attention..... OH and in this case size has NO bearing at all.