Also known as: Kata Gatame · Head-and-Arm Choke · Side Choke · Blood Choke (colloquial)
Trap their arm across their own neck, wrap your arm around both, and let their shoulder do half the strangle — usually set from side control or mount and finished after sliding off to the side.
Submission · Strangle (blood choke) · Gi & No-gi · Difficulty 2/5 · Usually learned at White belt
Starts from Side Control as the top player → ends the match (submission).
The details that make it work
Drive their near arm across their neck with your shoulder pressure, then dive your arm around head and arm together.
Lock palm-to-palm or bicep grip; your head drops to the mat on the far side, ear low.
Slide your hips OFF their torso to the choking side ("dismount") — the angle finishes what the squeeze starts.
Where it goes wrong
Squeezing square on top where their free shoulder relieves the pressure.
How opponents counter it
Answer the shoulder walk early — bring the trapped elbow back to the ribs
Bridge into the choke and turn toward the trapped side
Is the Arm Triangle Choke legal in competition?
Legal in all major rulesets at all levels (IBJJF, ADCC, sub-only). Rules change — always confirm against the current official rulebook for your event.