A kneebar (also known as legbar, kneelock or hiza-juji-gatame) is a leglock that can hyperextend the knee. The basic kneebar technique is similar to that of an armbar. The practitioner will trap the opponent’s leg in between their legs and secure the leg with their arms so the opponent’s kneecappoints towards the body.
The practitioner then applies pressure with their hips, forcing the opponent’s leg to straighten, hyperextending the knee joint. A variation of the kneebar is similarly accomplished, but instead of holding the leg with the hands, the practitioner will trap the opponent’s foot behind one armpit.
The Leg Lock game will continue evolving for the foreseeable future, with new submissions and their variations popping up all the time.
For instance, here’s a Heel Hook/Kneebar variation called the Outside Heel Bar – as demonstrated by the Ruotolo brothers on the video below: