The roundkick, also known as the wheel kick or roundhouse, is an important kick that builds the basis of any kicking martial art.
The roundkick is useful for striking practically any part of the body with high speed and power.
The roundkick should strike with either the shin, the instep, or the ball of the foot.
This is mostly seen in Muay Thai. The shin offers a very hard impact surface, resulting in less pain to the thrower of the kick and more damage to the target. When executed in this manner, the kick comes straight from the ground towards the target in a line with a slightly curved trajectory. The entire body weight is often thrown behind this kick.
Seen in most kicking arts, the instep offers greater range and precision than the shin. However, without padding, a roundkick thrown with the instep can result in pain and broken bones if applied to the opponents elbow, shin, or forehead without padding.
This is a very rare method of kicking seen in some forms of karate. The ball of the foot is less fragile than the instep, while still not as strong as the shin. This method allows for the range given by an instep roundkick, but with the impact concentrated in a smaller area. However, this kick can be injurious if the toes are not pulled back correctly.
In this depiction, one can see how the toes are pull back and above, rather than pointing.