heel hook

A heel hook is a grappling submission hold in which a fighter traps an opponent's leg and twists the heel, applying torque to the knee and ankle.

Common in Brazilian jiu-jitsu and mixed martial arts, it's considered dangerous because the hold can cause serious ligament damage before the opponent feels enough pain to tap out.

In rock climbing, a heel hook is a technique where a climber hooks their heel over a hold to gain leverage or stability: She threw a heel hook on the ledge and pulled herself up.