Knife fighting. Many hand to hand techniques can be adapted to be used in conjunction with a knife and vice versa. I personally like filipino combative arts knife styles, such as Sayoc and Kai Illustrisimo knife techniques. The multiple attacks implemented can be devastating.
Much is written about knife fighting in general and some say that "no matter what, you're gonna get cut" no matter how much you train. I agree and disagree. If you train a lot, then your chances of avoiding cuts and coming out of a fight unscathed, are probably high. But I've sparred with a fellow friend in the past, and though I have no formal knife training (my background is Judo and Iaijutsu), I was still able to induce several fatal stabs and cuts to my well-trained FMA friend. Probably just dumb luck, and we would have both probably died as a result of the wounds. However, I have seen my friend train with others and he can inflict something like 7 to 10 cuts in less than 2 seconds. It was pretty impressive.
I have only had one knife encounter, but I walked away from that one without suffering and wounds so that's my only live experience.
What I have been taught is: go for major and specific targets when possible: the throat, the eyes, the chest, abdomen, kidney area, thigh. To disarm or render another knife fighter disabled, sever the tendons of the forearm or hand. Also, cut the opponent where he least expects it; flank area, lateral side or behind the neck, brachial area.
For knife design, bigger isn't always better, but we are talking fighting knives now and I would prefer a light, quick, and balanced blade, with at least a 5" blade, rather than a heavy chopper (although the chopper would work too) I think the model GS might come to mind, but all Striders are pretty nicely balanced. I used to like the Americanized tanto blade a lot, but I now prefer a clip, spear, or recurved blade. I think tip, blade shape, and edge geometry are important in the design of a fighting knife. The less drag the better. I used to like the traditional Japanese tanto (still do) but there are better fighting knife designs. I also don't like thin grips, but the knife has to have enough of a grip that remains secure. Polished and poorly contoured grips, I don't like. These criteria are more for a fighting specific knife, but many of up just carry a small folder or fixed blade daily. I guess the saying "the best knife is the one you have on you" applies.
I totally advocate the carry of knives for the purpose of a defensive role. I mean, if you are confronted with someone who wants to kill you with a knife, and you don't have something better like a gun, and you don't have the option of walking or running away, then a knife is great. However, in my daily activities, I doubt that I will ever encounter a situation, unless I have a seriously disappointed patient! or a robbery ( who would want to rob a Chiropractor? The Chio down the street maybe?). But I like knives and I enjoy carrying then and using them. That is why, though it may be overkill, I will carry an AR clipped to my slacks.
You never know what can happen.