It's a broad question. As far as mechanics, a lot of kicks can be thrown from that transitional step.
But if we break it down further, It depends. It depends on the "who", the "when" the "in what", the "where". "the how" and the old "against whom?'
As for "the who". There are advanced Tae-kwon-do kickers who can hit you from anywhere.
Case in point - working in the forced busing days, high school kids had fights on a daily basis, some of them quite violent. One day, two of them were being arrested for fighting. They were both handcuffed (behind their back) and a BPD officer was walking them out to the wagon. Three of us were trailing behind them. The officer was in the middle and was holding each by the upper arm as they walked up a short flight of stairs to the exit. One of the kids, 17 year old Johnny D, had been training in Martial Arts since he was a wee kid. Really nice kid who had been defending himself from the other, a violent trouble maker. Johnny D could kick like all get out. The other kid was yelling at the officer during the whole perp walk, Johnny didn't utter a sound. At the third step Johnny raised his leg (behind the officer's back) and roundkicked the other kid behind the head. Just a snappy roundhouse, which he whipped back down and never broke stride. The trouble maker's head snapped, he yelped and stumbled. The officer jerked him back up. We had to peel off to the side, covering our mouths trying to stop the laughter.
It was one of the funniest (and coolest) things I've seen to this day.
So the answer to the question of "What kind of kick can you throw on a set of stairs while your hands are cuffed behind your back?" would probably be "that's a silly question" or no kick, not in in real life". But then, Johnny had some really skilled TKD and I saw it. (hell, I still laughed writing this)
As to the "in what" - , mechanics aside, what I'm refering to is in what kind of sparring are we talking about? Don't get me wrong, you can still throw anything you want, but If we are Karate/TKD sport sparring the answer might differ than if we are doing any kind of ring fighting or continous motion sparring (no stopping for points) Not that you can't throw it, but if it's easilly countered that might limit your options.
I should interject here that I've been using that step and kick for longer than I care to admit. I love it.
"The how" Joe Lewis used to use that step for a sidekick a lot in sport Karate. He was incredibly strong and incredibly fast. When he threw it - he stomped the floor with his steps. I mean really stomped it. He considered it "blasting off the ground" and said it should never be thrown "slowly, lightly or with compassion in your heart". Some saw it coming and blocked it. Some retreated. But the ones that blocked it couldn't use their arm again for the next ten minutes, or their shoulder or whatever, the ones that ran usually got caught and were sent flying - usually considered a push with no point awarded. But it shook them so much their game face would look different. It would look scared.
I spent many hours in my kitchen discussing this step and kick with Joe. He said that as much as he loved it he didn't use it often in ring fighting (PKA) because it was too easilly countered.
As to "the where" if it's outside the dojo "the where" means a lot. I live in New England. There's ice, snow and slush on the ground three months of the year. And I'm wearing boots. The boots change your timing because of their weight. The ice changes your traction in a fast step. I'm not saying it can't be done, but it becomes far less practical outside of the perfect conditions of the dojo.
"The when". If we're sparring and I catch you napping, or you're circling back and forth, or stay flat footed for a sec too long, or (obviously) you protect your head but pay little attention to your body, you're going to get blasted. (I'm still talking side kick here.)
If you're a counter figher who likes to counter kicks, especially sliding to my backside, I'm going to have to use it more judiciously...or get blasted myself.
As to the other kicks usually thrown from that step, again, it depends. When you throw the hook kick from a step-in-front cross step, if you're moving real fast and the hook misses - there's a beat where you're real vulnerable recovering. You can actually recover quicker if you were slightly below your top speed.
If you hit to the head, you're fine, but sometimes if you miss and hit the shoulder or a high guard (both of you with right side forward, say) your balance is throw off a bit if you threw really hard.. and sometimes takes two beats to correct.
But if you can really hook kick - it's as much fun as Christmas. No, really.
As was said - you can make that step behind your lead foot, in front of your lead foot, or just bring your feet together. Bill Wallace used to bring them together. He had tremendous success with that.
With a roundhouse - if you're stepping behind the lead leg, you sometimes either jam your kick or have to shave off part of the angle open to you. Long as you can do it, you can do it.
As to the "against whom". Other than a side kick, a hook kick or a roundhouse, I don't think you're actully going to land any others against a savvy fighter. Especially against a savvy kicker. You can throw them, sure, but I don't think you'll land them to often. Go try against a TKD guy who's a more experienced kicker than you. Betcha you won't try it again.
