It's a real burr under my saddle to realize that my only legal recourse in similar situations is to not even stand my ground, but to literally abandon the clients, run away, and hide without making any physical contact, so that there can be no question

You have another option -- to stand between your client and the attacker, making no threatening moves yourself, and make THEM be the one who initiates physical contact. (Works better if 2 or 3 of you form a human wall.) Then you call the police and press charges. This law cuts both ways.