What is an arm triangle choke?

The arm triangle choke (also called kata gatame or head-and-arm choke) uses your arm and your opponent's own shoulder to strangle them. From side control or mount, you trap their arm against their neck, wrap your arm around their head, and squeeze your shoulder against one side of their neck while their trapped shoulder cuts off the other side. The choke is incredibly tight when done correctly because you use their own body against them. Finish by walking your hips toward their trapped arm side and dropping your weight. The arm triangle is one of the highest percentage submissions from top position and works in both gi and no-gi. Common setups include trapping the arm when they frame against you and transitioning from mount when they try to push you off.