My understanding is that using even one's hands when trained in martial arts, can be construed as responding with unreasonable force. I have to admit that I would rather err on the side of the attacked than the attacker. That being said, if the attacker is a "victim" of some crime such as physical or sexual abuse (example spouse or child) then I would fall back to the idea that their response was in effect "self-defense".
I have little sympathy for those who are into making others hurt. Yes, I know, that they have all had rotten childhoods and have all been victims themselves. But, this is not good enough to excuse "choices" that they make in the present. We operate to remove cancers in the body, we remove rotten fruit and vegetables from the storage bins in order to protect the healthy fruit, we repair through replacement, wood, metal and concrete our structures. This is nature. Perhaps there is a higher morality in natural law than in social law. Survival of the species is not about survival of individuals, unfortunately. The fittest is not just about physical, it is also about communal, social, moral and ethical concepts that ensure the strongest possible suvival opportunities of humankind.
We become weaker when evil is given more rights ensuring that the path of darkness and destruction is sanctioned and nourished by social and legal societies.