Half Guard — Bottom

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Half guard bottom is the position in which the bottom player has both legs wrapped around one of the top player’s legs, trapping that leg between their thighs with the feet locked or crossed. The top player has effectively passed one side of the guard — their other leg is free, their upper body is over the bottom player, and they are working to complete the pass or establish side control. Half guard is not full guard that has been weakened. It is a distinct position with its own logic, its own attacks, and its own failure states.

The defining feature of half guard is the underhook battle. The top player seeks to get their arm under the bottom player’s near arm, flatten the bottom player, and advance to the pass. The bottom player fights to get or retain the underhook on the same side — the arm under the top player’s armpit on the trapped-leg side. Whoever wins the underhook controls the hip on that side, and hip control determines what each player can do next. This is not a secondary detail of half guard. It is the central contest.

Half guard uses the same invariants as full guard. The difference is that one side of the foot and knee line is already conceded before the exchange begins — the top player’s leg is trapped, so that half of the guard is partially resolved in the top player’s favour. The margin for error on the remaining connections (the underhook, the frames, and the bottom player’s hip mobility) is therefore reduced, not that different principles apply. The same rules govern both positions; in half guard, one of them is already partially lost.

Ruleset contextADCC Legal No restrictions on half guard bottomIBJJF No-Gi Legal The Invariant in Action

INV-G01Invariant "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."

Why it works hereHalf guard begins with one side of the foot line already conceded — the top player's leg is captured, but their other leg is past the line. The remaining leverage lives on the free-leg side and on the upper-body connections; that means every other connection has reduced buffer. A weak underhook in full guard is recoverable; a weak underhook in half guard, combined with the already-conceded line, puts the pass one motion away. Treating the position as full guard with reduced margin, not full guard minus one element, calibrates the urgency correctly.

See full invariant page → In half guard, one side of this line is already conceded. The top player’s trapped leg is between the bottom player’s legs — that side of the foot line is resolved in the top player’s favour. The bottom player’s remaining leverage is on the other side: the free leg can post, hip escape, or attempt to re-hook. The consequence of this partial concession is that the margin for error on everything else is reduced. In full guard, a weak underhook is manageable because the foot line is still fully intact. In half guard, a weak underhook combined with poor frames means the pass is very close to complete. The bottom player is operating with reduced buffer on every connection.