Underhook Half Guard (Bottom)

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Underhook half guard is the offensive configuration of half guard bottom. The bottom player has one arm inserted under the top player’s armpit — on the same side as the trapped leg — with the shoulder pressing into the top player’s chest and the hand reaching behind the top player’s back. The bottom player is on their side, not flat on their back. The hip that corresponds to the underhook side is off the mat. The leg trap is in place.

The critical distinction is between underhook half guard and crossface half guard. These are not two equally valid positions — they are the offensive and defensive positions of the same configuration, respectively. When the bottom player has the underhook, they control the near hip and the near shoulder of the top player. The top player cannot flatten the bottom player easily; they cannot advance without first dealing with the underhook. When the top player has the underhook (the crossface), the situation is reversed: the top player controls the bottom player’s near shoulder, the bottom player is being pressed flat, and the pass is very close to complete. Underhook half guard is not half guard — it is winning half guard. Crossface half guard is losing half guard.

The underhook is the foundation of the entire half guard bottom offensive system. The dogfight stand-up requires it (standing without the underhook is standing into the top player’s front headlock). The lockdown works best with it. The underhook sweep requires it directly. The back take from half guard begins with it. Practitioners who understand that half guard is fundamentally an underhook battle — and who prioritise getting and keeping the underhook above all other concerns — will find that the specific sweeps and exits become almost secondary. The underhook is the enabling condition. Everything else follows from it.

Ruleset context This technique is legal in all major competitive formats.

INV-G03Invariant "Connections to the inside of the top player's elbows — or to the outside of the elbows — control the top player's weight distribution and passing options. Losing both connections simultaneously is the guard being passed."

Why it works hereThe underhook is INV-G03 made into the central battle of half guard bottom — an arm under the top player's armpit on the trapped-leg side that connects to the inside of the near elbow and shoulder. While that connection is alive, the top player cannot drive their weight cleanly into the bottom player's chest because the shoulder is being kept up. Losing the underhook to a crossface is functionally losing both connections on that side; the underpump and immediate hip escape are the recovery procedures, but they only work if launched the moment the underhook is lost rather than after the flatten completes.

See full invariant page → The underhook is elbow connections made concrete in the half guard context. Getting the arm under the top player’s armpit is establishing a connection to the inside of the top player’s near elbow — to the inside of the near arm — that controls the near shoulder and, through it, the near hip. This connection does two things simultaneously: it prevents the top player from driving their weight into the bottom player’s chest (which would flatten them), and it gives the bottom player a directional handle to redirect the top player’s momentum. When the bottom player has the underhook and is on their side, they are not defending against the pass — they are threatening the sweep and the back take. The underhook is the difference between a guard that is being passed and a guard that is attacking.