"... although your back will be to your target."
Yeah, that's how I envisioned it -- to be able to simultaneously turn around and face someone else. Of course, I might say that at some -SM I could spin the other way to begin with, back first such that I can't see my target in order to end up facing him afterwards, but I've got an acrobatic bod-heavy endgame in mind that will incorporate several positional tactics including rolls and flips but not excluding those which affect my opponent's position (7@2) with my already nod-worthy martial arts prowess, so that's not really the direction I want to take this anyway.
Damaging on failure sounds good, but I would say that in a combat situation even if fall impact avoidance is successful I'll need to use my 4@4 instant stand to get up faster than the usual :18 - :60 seconds.
My thought for how I would end up on my feet again involved the idea that once I had hit his legs I wouldn't immediately let go and would instead push of in an *upward* motion such that my legs would go *down* and I could then land, crouching, on my feet. If the envisioning involves hitting leg (as opposed to targetted attack only against knee, as it could involve hip or muscle pain against thigh), my small size (4'6") might make it easier to do such a thing; one might either leave it up to relative success or note it as a possibility for the professional or expert.
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I'd like to fall on success for annoying damage. I've got the positional combat training and instant stand should more than make me comfortable. The fall on failure should be damaging. it might be easier (thus either mitigating some penalty I don't yet know about, or providing some bonus for departing from the baseline, or providing some bonus elsewhere in the skill -- not damage, perhaps duration if the question applies) to simply go down with him and worry about the instant stand.
As to the classification of the skill itself, I would probably classify it as Kick, but also Grapple (it is something of a grab, and I might eventually take advantage of that factor), and definitely what we call Poke (because it's clearly the kind of ability that requires humanoid anatomy -- while I could use it against, for instance, a centaur, I'd be penalized, I probably wouldn't knock him down, and then he'd probably trample me; it's a really bad idea).