Interesting. I would love the long version. Thanks. When you have the time.
YES! I was hoping you'd say that! (I don't know why I derive such pleasure from discussing the nuances of the differences in training and execution of Tsukahara and Kazamatsu vaults, but I really and truly do)
ANYWAY
First thing you need to understand: a left-footed roundoff is not twisting to the left; it's twisting to the right. For a further explanation, check out
this video. The rest of this explanation will make zero sense until you have internalized this oft-misunderstood fact.
The Kazamatsu is a 1/4 on followed by a salto with a 3/4 turn in the opposite direction. It is scored the same as a tsuk 1/1, and to the untrained eye looks like the same skill, but it is actually completely different (and, in my opinion, MUCH easier to train).
So what's the best way to train it? It depends on who you ask. My preference is to train it as a tinsica followed by a front 1/2.
For the sake of this example, we'll assume a gymnast who does a right-handed roundoff and twists to the right.
First and most obviously, the gymnast should have strong front handspring and roundoff vaults. They should be capable of, at the very least, doing a tsuk or a handspring front into a pit with a strong block. The gymnast should also be comfortable doing a front 1/2 (NOT a roundoff in the air, but a front 1/2 -- very important that this twists the same direction as all her other twisting skills) into a pit, and spotting the landing. If she can land it on a mat or on floor, so much the better.
At this point, I would have the gymnast work a tinsica on floor. The gymnast should start just like a roundoff, but rather than completing the twist to the left to finish facing the way she came from (as she would for a normal roundoff), she switches directions when her hands contact the floor, and turns back to the right to finish facing the same direction she was when she started. This twist is accomplished with a strong push behind the head with the left arm, and the gymnast should land with the left arm still up (the right arm will generally be somewhat out to the side on the landing). The head should be up, similar to the landing on a front handspring.
This skill may seem awkward on floor, but bear with it; it works spectacularly on vault.
Next, I would have the gymnast do a tinsica on vault (ie 1/4 on, 1/4 off to land facing away from the table) to land on mats stacked to around table height (the higher the better). As on floor, she should land with the left arm still pushing up and back, the head up, and the right arm out to the side. It is very important that the gymnast keep the left shoulder fully extended for a powerful block off the left arm.
The great thing about this is that once you get this technique down, you can get some MASSIVE block this way -- it seems like many gymnasts can get significantly more pop on this sort of vault than they can on a roundoff or front handspring vault.
For the next step, there are two drills that ideally should be worked in parallel. First and most importantly, the gymnast should work the aforementioned tinsica vault followed by a front tuck. For this, I tell my gymnasts to think about squaring it up like they're going to do a front layout before they pull the tuck. One correction I was given on my own Kaz-entry vault (by Slava Boiko, assistant men's coach at Penn State) which I've found particularly useful is to think about driving the heels down and hips up as the gymnast comes off the table.
The second drill I would have the gymnast work on is a double front 1/2 out. This is the less important of the two, but is generally helpful for building the gymnast's confidence and aerial awareness.
Finally, put the two together. Tinsica in, spot the ground, front 1/2 out. And there's your kaz.
The most common error in this step is doing the final 1/2 too early. The gymnast should be sure to spot the ground before initiating the front 1/2, and should maintain visual contact with the landing for the rest of the skill.
Done properly, it is actually much easier and less scary than a regular tsuk in my opinion, as it allows the gymnast to spot the landing almost immediately after leaving the table, and she can maintain visual contact with the ground for almost the entire postflight.