What is scarf hold in BJJ?

Scarf hold (kesa gatame) is a pinning position from judo where you sit beside your opponent, wrap your arm around their head, and trap their arm under your armpit. Your hips stay low and heavy. It is incredibly controlling - opponents feel like they are being smothered. Scarf hold sets up arm locks and transitions to mount or north-south. Some people avoid it because it can expose your back if done incorrectly, but when applied well, it is one of the most oppressive pins in grappling.