Many of those who challenge nonviolence assume that one is startled and threatened and one must either react with violence or be vulnerable. This assumption is often quite false and it is likely that those who are untrained in either violence or nonviolence will be the most vulnerable. Those trained in violence or nonviolence are most likely to prevail in the moment, and those trained in nonviolence can expect to do better in the long term.
Some claim to have a martial art that is nonviolent, and some individuals may well be quite adept at that. Some get your attention by claiming nonviolence and then you discover them tossing others to the ground, inflicting pain, and even hitting others in the face. Not exactly nonviolent.
Psychological defense is the best with humans. The closer we can come to matching the cultural make-up of the attacker, the more effective we can tailor our response. When we speak the same language in every respect, we can disarm another with relative ease--if we decide that is our goal.
In a negotiation--and that is what most attacks are, in a sense--using the same principles as those martial arts are the psychological equivalent to the principle of using the force of the attacker to de-escalate instead of escalate the conflict. Roger Fisher, Bill Ury and Bruce Patton have now given us the third edition of Getting to Yes and it polishes these ideas. They advise three tactics.
Look behind the attack to find the interests the attacker is attempting to satisfy.
Don't attack back. Invite criticism and ask advice. I accidentally used this once in an actual mugging in Roxbury, Massachusetts. I was surrounded by three young men late at night and they told me to give them money. Rather than meekly do so, and rather than risk a beating for not having any, I shot back, "Do I look like someone with money? I mean, you can have it, but you guys need to know that I have two kids and no money!" I gave them literally all I had on me, less than $2. They let me go, almost shamefaced.
Recast an attack on you as an attack on the problem. I could have said to those young men, "I know what you mean. I have a family and no money."
Asking questions helps guide attackers away from you, especially if the attack is not about resource capture but is rather about defending personal pride in some way. They may not be articulate or they may believe that you aren't listening. But if you ask and then actually prove you are listening, hearing, and able to reflect their assertions or even demands accurately, they will be less likely to be motivated to take it to the next step, the physical attack.
Nonviolence works and violence works. But when your weapons are your mind and your communicative abilities you tend to stay well armed and prepared to respond to attack at any time.
Fisher, Roger, & Ury, William (2011). Getting to yes: Negotiating agreement without giving in. (3rd ed.). New York: Penguin.