The roundhouse kick of (?) karate is called (?). And as the name suggests, it comes around and hits the target to the side. When we're developing it with our basics, we're going to hit with the ball of the foot. During sparring with our partners in the dojo, we use the top of the foot. It's a little bit less dangerous, because you can slap a little bit without too much damage. Whereas the ball of the foot, anywhere here, is going to be extremely penetrative and dangerous.
Also in competition, it gives a little bit more reach. It's probably the most common kick in competition, because it lends itself well to a slight variation. For example, you can come a little bit straighter, and then flick it around on the end. And the legs are so strong that a little flick has a great effect. In streets however, I'd kick much lower. And I'd use the ball of the foot. If you're wearing shoes, of course, you're going to hit with the tip of the foot.
But in karate practice, generally, basically, we're going to do the ball of the foot. Like (?), where you want to squeeze it up this way, we're going to squeeze it as close as we can to the side. So obviously that's going to involve not so much your stomach, but your obliques. Your hip is going to turn to hit the target this way. So if you don't turn your hip, you're going to swing your foot across. That's neither here nor there. There is a crescent kick, but that's tricky to apply. (?) really requires a huge rotation of the hip.
And like other techniques, you have the feeling that you're actually going to make contact with your hip. And you've got a leg on the end of it. So be careful of striking first, and then flicking your foot on the end. Which will only work if the timing's right. If the opponent moves in a certain way, you hang back, and flick at the end. But when you're building your basic pure form, you really want to bring the leg around as a unit. With the whole body. So make contact at the end. And the feeling is you've actually hit with the hip.
So this is (?), the round kick, (?), of (?) karate.