I was in Germany with a group of martial artists teaching "street knife work." While demonstrating an empty-handed with one of them, he tackled me and took me to the ground (This is no big deal as when I do demo's I don't allow "courtesy attacks." I insist people attack me like they would were it a real fight -- this occasionally means that I get slugged or taken down. This was one of those times). Anyway, when we hit the floor I realized that there was no way I could contest this guys strength, he was a bull, full of muscle and grappling skill. The thing was I had landed next to a practice knife that I calmly picked up and dragged it across his throat.
We stood up and his eyes were the size of saucers because he realized what the significance of what had just happened. A knife had come out of nowhere and had this been real, he would have been dead. The amazing thing was is there were only a few other people there who did too. On of the bigger proponents of grappling stood there and said, "He tackled you." To which I replied, "Yes, and I slit his throat" "But, he tackled you."
Ghu knows, I'm not qualified to judge the accuracy of this (I study t'ai chi for health and the fun of it ), but nothing in it sounded implausible. Those of you who study a martial art, have you been taught how to hit while moving? Were the legal issues associated with hurting someone mentioned?
I did study kenpo for about six weeks, and one of the first forms I was shown included at least one foot stomp for after my hypothetical attacker was on the ground. There was no mention of legal issues.
 This reminds me that there was a time when I studied T'ai Chi simply because it improved the day. Now there's an element of panic at how much I stiffen up if I don't do T'ai Chi or qigong for a couple of weeks. Fuck. From one angle, I should count my blessings-- at least I've got T'ai Chi-- but I'd forgotten that there used to be a lot less worry associated with it.
Link thanks to yhlee. By the way, most of her interesting links are grouped under "webreadings". I can't think of anyone else who has a blind link like that which is generally worth clicking on.