The chudan mawashi geri — the roundhouse kick to the body — is one of the highest scoring techniques in competition kumite. It is also one of the easiest to throw in a way that a judge will not reward.
Here are two versions of the same kick, compared.
Lower-body mechanics and centre of gravity
The weaker version: the centre of gravity rises during the attack. The rear heel lifts early, so power leaks upward. The hips travel after the hand, and the weight shifts too late.
The stronger version: the centre of gravity stays low and stable. The rear leg drives first — ground, then hip, then hand. The hips initiate before the arm, leading to a clean forward weight transfer.
In kumite, power must come from horizontal drive, not vertical bounce.
Hip and shoulder sequencing — the kinetic chain
The weaker version: the arm leads the technique. The shoulder rotates independently. The hip line and the shoulder line are disconnected.
The stronger version: the hips rotate first, and the shoulder and arm follow naturally. One connected kinetic chain.
This is the part that decides the score. Judges reward techniques that show body-driven force, not arm punching. A kick that arrives without the body behind it reads, correctly, as a touch rather than a technique.
What to work on
If your kick is not scoring, the problem is very rarely the leg. Look at whether the hips are arriving before the limb or after it, and whether your centre of gravity is travelling forward through the target or upward away from it.
Fix the order in which your body parts move, and the kick fixes itself.