Targets for the round and Thai kick

The Thai and roundhouse kicks (some styles (JKD) name this the hook kick as well) are probably the most versatile in our arsenals. It can be thrown with such speed, without a windup, and at almost any angle. No doubt, it should be considered one of your primary weapons, whether for self-defense, combative (military close-quarters) applications, MMA, or any other type of competition.

The round kick can also be thrown to nearly any target outside of the centerline. Let's examine some of the general targets:

Head and neck

All head attacks can be unpredictable; a blow to the head could yield an instant knockout, or have no effect. A roundhouse/Thai kick to this location is a relatively low-percentage attack because the head is relatively well-defended, and the the furthest target from the starting point of the technique (the ground). Kicks here should be used as a surprise, not as a staple of your arsenal. The benefits are that the temple, behind the jaw, and the side of the neck will usually yield a mild stun or knockout. Even a light, quick round kick to the head can floor someone.

For self-defense and combative purposes: I actually like the head kick a lot - as a surprise technique. Set this up by leg-kicking a lot. After slamming the leg kick a few times, your opponent will only be focused on defending down low when he sees you telegraph it, and that's when you should unleash the head/neck kick. If you overuse this kick, it will be your downfall, quite literally. I have fallen when using it in a controlled environment, and that could be lethal in a self-defense situation. Terrain (slick or not) and gradient (hilly or flat) play a large factor in whether to use this technique in self-defense. Some would say head kicks should only be done when your opponent is down, but that dogmatic approach doesn't always yield the best results.

Cautions: without control in sparring, this kick could severely hurt your partner. In self defense, a head kick, and uncontrolled fall can look bad to onlookers, especially if the attacker busts his head open on the pavement, leaving you open to criminal and civil liability. Use your best judgment here, folks.


Shoulders and arms

High percentage, but not recommended are kicks to the shoulders and arms, unless you're wearing heavy boots. Keep in mind that my perspective is self-defense oriented, so I always train with shoes now.

For self-defense and combative purposes: I wouldn't do it much. The target is too high, and the payoff is too low. The most you can reasonably hope for is stunning the arms, and the worst-case is that you fall on your butt, or that your leg is caught and you're dumped.

Cautions: there aren't really any dangers in doing this, except hitting an elbow, which, when training barefoot, can dampen your enthusiasm for kicking for a few minutes.


Trunk and hips

This should be a great target area - it's large and hard to defend the entire torso, but I don't recommend it unless it's from the correct angle. If your opponent is perpendicular to you, a great attack is to use the ball or toe and go right into the solar plexus, bladder, or groin. This is a medium percentage attack, and can do a lot of damage. Some of you are quick enough to hit the ribs when an arm is extended, but I only use that when I'm sparring and my opponent is expecting a head kick and extends his arms.

For self-defense and combative purposes: The groin and bladder are always great targets, but be careful of getting your leg caught. If you're wearing heavy boots.

Cautions: Same as shoulder and arms.


Thighs and calves

This is the best target, percentage-wise. A leg is almost always open for attack, and it's the quickest of the round kick targets, being level with the beginning of the technique. It's also great for setting up higher attacks, or even takedowns in sport applications. Aim for the spot between the quadriceps and hamstrings (peroneal nerve) when attacking the outside of the thigh, which can result in spasms in the leg, and mentally stun your opponents. To the inside of the thigh (femoral nerve), a round kick can cause severe pain and motor dysfunction for several seconds. The calves and shins are easily attacked as well, with nearly equal effect.

For self-defense and combative purposes: The legs are your best bet, and there are no downsides. There is little cost to you in terms of overcommitment or loss of balance, and this can be your fastest kick. Highly recommended for the reasons listed above.

Cautions: Again, few cautions here. Only worry is if you don't wear shoes. The advantage of kicking low is that you have more targets, and more predictable effect, with little chance of causing death or severe injury. My only worry would be kicking to the back of the legs can take down your opponent and cause severe injury.


Summary

Keep 'em low, but sneak em up. Hit hard and fast, and keep your feet on the ground most of the time.

UPDATE:
Fightclub.Gaijindo.com has a nice example of the round kick in sparring. An even better one here.