Learn the knee slice (knee cut) in BJJ: head and hip position, the cut across the thigh, 3 points under IBJJF rules and the mistakes that send you back.
The honest answer: the knee slice, also called the knee cut, is a guard pass in which you cut your knee diagonally across your partner's thigh and land in side control. It is a classic pass you find in both gi and no-gi. Under IBJJF rules a guard pass scores 3 points once you hold side control or north-south for 3 seconds [1].
The pass sounds simple and still feels like a six-piece puzzle in your first week. Expect weeks until the basic movement sits and months until you get it through against equally experienced partners. That is experience, not a study.
What we know: whoever plays the pass fluidly wastes no energy. In competition BJJ fighters work at roughly 6 seconds of action to 1 second of pause, and the intense actions last about 4 seconds [5]. A pass that lands in 4 seconds is exactly what a match demands of you.
Get low, chest down, head in contact with your partner's head, hips close. You make yourself small and heavy, not tall and wide. Whoever sits up gets swept. Milestone: you hold the position for 30 seconds against a cooperative partner without them getting an underhook.
With shoulder and forearm you pin your partner's upper side so that their knee shield does not stay between you. The pressure goes through shoulder and rib cage, not through sharp elbows. Hands that block the nose or mouth are prohibited under IBJJF rules [1].
Now your knee slides diagonally across your partner's thigh. Your shin lies along the thigh, your weight stays on the hip. Imagine a knife gliding through butter: it needs angle, not force. Your eyes go to your partner's hip, not to the knee.
Your trapped foot comes out by turning it out, not ripping it out. The hip follows the knee. If you rip, you twist your own knee, and that is among the most frequently injured regions in BJJ [3].
You close chest and hips, control head and hips and hold for 3 seconds. Only then do the 3 points count [1]. If you lack stability you get at most an advantage point when the pass almost lands [1]. If you then do not seek progress in side control, you risk a penalty for lack of combativeness [1].
Practice in three stages: cooperative, then light resistance, then free resistance. Move on only once you manage the first stage cleanly 3 times.
The slice looks harmless but loads two places: your own knee and your partner's rib cage. The knee is the most affected region at 25 % among 881 BJJ practitioners surveyed worldwide [3], and 79 % of training injuries happen in sparring [3]. So dose your pressure, especially against lighter or new partners. When you feel a tap, release at once.
Cut slowly and in control while your foot is still caught. The momentum belongs in the hips, not in a jerk at the knee. This does not replace supervised training: learn the pass with a coach.
Do not wait for the knee to "cut". The pass is born in head position: if your head is already where the hips want to go, the rest follows almost on its own. Many advanced players do not lose the pass at the knee but just before it, because the head still hangs in the middle.
A guard pass in which you cut your knee diagonally across the opponent's thigh, free your foot and land in side control. It counts as a guard pass.
As a guard pass, 3 points once you hold side control or north-south for 3 seconds. If the pass does not become stable, there is at most an advantage point [1].
For everyone who can open closed guard and control half guard. It is an intermediate pass because head, hips and foot have to be right at the same time.
It loads your own knee if you rip the foot out instead of turning it out. Knee injuries are common in BJJ [3]. With calm hips and a coach the risk is manageable.
De La Riva Guard in BJJ: The Outside Hook Without the Knee Stress