Considering ukigoshi, if you look at uke and tori from above you can imagine them as gears turning together. One typically has to turn faster and farther than the other, thus creating different forms of throws. For example, sometimes tori turns a lot while uke doesn’t turn much, creating the big hip throws like ogoshi and koshiguruma. In other instances, tori turns a little as uke spins around him, creating different hip throws, like ukigoshi and haraigoshi. Most often it is some middle condition, with tori and uke each making some part of the turn. This variation in the turning speed of the two ‘gears’ is called gearing ratio, and you can get more info on that at wikipedia.
With that in mind, you can define about two basic forms of any koshinage:
- Catch uke stepping forward. Step to the side just as his front foot plants, pulling him into offbalance. Turn your hips backward into uke with a backstep, loading him and throwing.
- Catch uke stepping forward. Step to the side just as his front foot plants, pulling him into offbalance. Pull uke’s lapel side 90 degrees to get him to step with the other leg. Load him onto your hips and throw as he turns the corner.
In the first form, tori makes all the turn as uke hovers in offbalance. This is the form classically taught in uchikomi, with tori pulling with the left arm and turning in to catch with the right arm. This is also the form taught in amateur wrestling – called something like ‘the back-step’. In the second form above, uke makes part the turn as tori makes the other part of the turn. As tori is turning to the left, uke is stepping with his left foot, taking up the slack.
Both forms are decent beginning ways to learn the thing. I alternate between them in my teaching. I often teach the back-step technique as kubinage instead of ukigoshi or ogoshi – but that’s just a preference thing. There are many variations, but they mostly tend to fall in a spectrum between these two basic forms. In randori situations you have to find the right middle-ground between these two basic forms on the fly. That is just part of the art of the thing.