The feet should stay on a line that faces the passer

"The bottom player must maintain their feet between or at the line of the top player's knees. Losing this line allows the top player to advance without engaging the guard."

The foot line is the guard’s outermost barrier. When the bottom player’s feet are between or at the top player’s knees, they create a structural obstacle that must be addressed before the top player can advance. The feet — whether placed on the hips, thighs, or floor — hold the top player at distance and force them to engage with the guard on the bottom player’s terms. The foot line is not decorative; it is the first load-bearing element of every guard position.

The line is spatial, not grip-dependent. It does not require a specific grip or hook — it requires the feet to occupy the space that prevents the top player from simply walking through. In open guard, the feet frame against the hips or shoulders. In closed guard, the locked legs enforce the line passively. In half guard, one side of the foot line has already been conceded to the top player, which is precisely why half guard is a disadvantaged starting point — INV-G01 is partially resolved before the exchange begins.

The foot line is not about keeping the top player at maximum distance. It is about ensuring that the top player cannot advance their hips past the feet without first dealing with those feet. When the feet are retracted, dropped to the mat, or allowed to drift outside the knees, the structural barrier disappears and the top player can advance freely into the next control position.

Across the system, this principle expresses most cleanly in the following techniques:

De la Riva guard: The hooking foot lives at the line of the standing top player’s knee. The other foot stays active on the far hip or biceps. As long as that line is held, the top player cannot drive their hip past it. The moment the DLR hook drops below the knee or the second foot retracts, the passer’s lead leg clears the line and the pass begins.

Butterfly guard: Both feet sit between the top player’s thighs at knee level. The bottom player’s foot line is the engagement — without it, the top player walks straight into a flattening pass. The whole guard depends on the feet maintaining contact at the line where the top hips would otherwise advance.

Single-leg-x: The bottom player’s feet split the top player’s lead leg, with one foot at the hip and one at the far thigh — the foot line is wrapped around a single leg. The top player cannot advance because their lead hip is captured between the two feet. Losing either contact point releases the line and the top player steps free.

Z-guard / knee shield: The shin across the top player’s chest is the foot line raised to knee level. As long as the shin is connected and the foot is hooked, the top player’s hip cannot slide past it. Once the shin slips down to the belly or the foot loses its hook, the top player flattens through.

Seated guard: The bottom player’s feet are active and posted between or at the line of the top player’s stance. The whole engagement is a contest for whether those feet maintain the line. When the seated player’s feet drift outside the top player’s knees or get pinned to the mat, the passer steps in unopposed.