I teach two types of kicks.  Maiming kicks and friendly kicks.

Friendly kicks include swipes, sweeps, traps, stops, and ways to get your partner's legs jumbled up so they fall down.

Maiming kicks are designed to be used only once.  They usually sever or snap ligaments.  Sometimes they tear tendons, and sometimes they break bones. When they break bones it is usually a small bone like a collar bone, pubic bone or a bone in the foot.

I've never actually used a maiming kick to maim, but I'm pretty sure they work because I've almost had my ligaments snapped a few times.

These two types of kicks go together.  You practice the friendly ones at real speeds and the maiming ones at gentle slow careful speeds.

Both of these technical categories are different than most of the kicks used in sparring.