Osu! The mawashi geri is a basic technique, but truly one of the hardest to master. I find that one of the hardest things to overcome when throwing a technique is the tendency to "muscle" it, rather than move from a place of relaxation. Some of the best kickers in the Kyokushin game have a seemingly effortless, flowing rhythm that directly influences their sudden and explosive emissions of power. When kicking, as previous posters have explained, its very important that the supporting foot is turned out so that the hips open up and roll over. Also, stepping towards your target at angle (not directly towards) helps send the energy of your kick on the right trajectory. As for the kicking leg, think of it as loose and flexible, like a whip. Many of my students (even pretty proficient kickboxers) use their kicking leg like a stiff baseball bat. While this is certainly painful, its demanding on energy levels and it lacks the destructive power of a quick, sharp, cutting technique. In all your practice, always remember to issue your techniques from stillness, and to strive for relaxation. Keep training, and I promise you'll find it! Osu!