Kneeling is mainly used as a transitional stance to enter or exit seiza, but has some fighting applications. Kneeling allows you to recover from a breakfall or drop kick without using your hands, meaning you can block while you recover, minimizing your vulnerability. Kneeling can also provide extra downward momentum to drive some takedowns.
Your leading leg should have a 90° knee bend; your shin is perpendicular to the floor, and your thigh is parallel to floor. The shin of your trailing leg rests on the ground, with your knee directly under your hip. Your trailing leg's ankle is directly behind its knee, with its toes and the [Koshi|ball of the foot]] touching the ground (“active toes”). Your instep does not contact the ground, because it is harder to stand or maneuver with “seal feet.” The leading heel and the trailing knee are a shoulder-width apart. Naturally, your shoulders remain above your hips, to ensure maximum stability.
Alternately, one can easily enter a correct kneeling position by entering a horse stance and twisting 90° while sinking, like a corkscrew.
[photo of kneeling from the front and side.]