A kick to the opponent's thigh delivered with the shin. A core weapon in kickboxing and Muay Thai.
The low kick works cumulatively: a single one rarely ends anything, but after five or six the opponent's lead leg stops carrying properly and their mobility collapses. Technically you strike with the hard shin, not the instep, and power comes from rotation — support foot pivoting on the ball, hip driving through, the kick travelling through the target rather than stopping at it. Two things matter: first, your lead hand drops almost automatically as you kick, inviting the counter right — keep the guard up. Second, the shin is sensitive early on; conditioning happens over years on pads and bags, not through quick hardening tricks. Rules note: low kicks are illegal in Olympic taekwondo and in many kickboxing rule sets (point fighting, for instance) — always check your discipline's rules.