Outside of that, one of the first things I learned is that kuzushi refers to "unbalancing your opponent." This is, by far, the most common definition of the concept I've heard over the years.
The next thing I learned is that there's more to it than that.
The word itself, according to Wikipedia anyway, "comes from the intransitive verb, kuzusu, meaning to level, pull down, or demolish. As such, it is refers to not just an unbalancing, but the process of getting an opponent into a position where his stability, and hence ability to regain uncompromised balance, is destroyed."
Well, that's certainly a good reason to think of kuzushi in such terms. But based on the myriad of things taught to and shared with me over the years by budokas far more advanced than I (or even will be for several more decades), I've come to realize it can include much more.
For example, kuzushi also seems to mean:
Forcing uke to take a step or make an action he didn't intend to make
Perhaps I simply step off the line of attack, even without touching my uke, and now he has to reorient himself on his original target (me) in order to continue his attack. Therein lies an opportunity for me to do any number of things.
If in judo, perhaps I give a quick little tug on my uke's collar, causing one foot to step forward, and as it does, I sweep it out from under him.
Or all I may do is lean a bit on the collar grip, loading a little weight into my partner's back foot. When I release that slight pressure, he can't help but "bobble" forward a tad. That unintended forward momentum, however slight, is an opportunity for me.
Limiting uke's options
If budo randori were a chess match, these sorts of applications would be the "check." The game isn't over, but the King had better do something, or he's going to get "got" in the next move.
For instance, while it may seem like a "dirty trick", there really is something extraordinarily effective about stepping on someone's foot and keeping it there. Suddenly, your attacker can't go anywhere, and he's now down to three appendages instead of his customary four. And if I happen to be standing more to his side than in front of him when I step on his foot, he will also have a difficult time reorienting his remaining weapons in my direction. Sucks for him, but yea for me.
In my early days of aikido training, I would very often find myself in the same position over and over again when practicing randori with a more advanced partner: him standing behind one of my elbows, with his hand just behind the notch of my elbow, and me, completely unable to turn around.
Or think about kote gaeshi as less of a "throw" and more of a sort of hold. There have been many times in randori where I've held my partner's wrist in kote gaeshi, but without them ever falling. I didn't, however, just abandon it—why should I let him off the hook? His posture was crimped, and his free hand was limited in it's effectiveness, because he knew (or sensed) that whatever force he applied with it would come back to the hand held in kote gaeshi. In which case a fall would be the likely consequence.
Forcing uke to focus on something that occupies his attention
One of the most infuriating things you can do to an opponent in grappling is to grab a hold of him somewhere, say his arm, with two hands in one spot, bring your hands to your body, and simply let uke spend all kind of energy just trying to get his dumb arm free.
Or maybe you casually slip a hand inside the collar of his gi. You're not in a position to choke him, mind you, but many less experienced grapplers will nonetheless feel threatened, and begin to worry about that hand. Meanwhile, you proceed to nab an arm bar, and before he realizes what's happened, he's tapping.
It can even be, I believe, an action as silly as pointing over uke's shoulder and exclaiming, "What the hell is THAT?!?" and when he turns his attention away from me for even a split second, again, therein lies an opportunity. Now, some may think that's some form of cheating, or just not "proper budo," but really, when it comes down to two people trying to kill each other (it's a martial art, right?) I'm willing to bet you'd use whatever tool you had at your disposal to make sure you lived through the encounter.
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What do you think? Did I leave anything out? Is any of that kuzushi to you? Or would you define any of it as something else?