A very powerful attacking tool, the Crescent Kick gets its power from the sartorius, illicus and tensor fascia latae muscles as well as the hamstring and groin area. As effective a stretch as it is a kick, the Crescent Kick is a tremendous aid to increasing balance.
The practical application of the Crescent Kick is when in close quarters with an opponent, delivering a strong blow with the side of your foot to the face. Without flexibility and a good stretch, this kick is hard to throw, but if you have these qualities, then the Crescent Kick is a terrific addition to your arsenal of techniques.
The mistake which almost always happens when performing this kick is using just the leg to generate speed without torquing the hips and waist, as well as leaning the torso too far forward (usually done to compensate for lack of stretch). Either mistake will rob the kick of both speed and force, making it less effective than it could be.
Inhale before you kick and as you perform the kick, exhale sharply. When you return to ready stance, inhale again.