Learn KUNG FU OnlineJam Sau 枕手 (sinking block) is useful for crushing the structure of frontal grabbing arms. Can also be used for deflecting straight low shots downwards using the forearm bone, without needing a clean catch in the hand as in Pak Sau, in case the hand is injured or holding something.
It’s generally done from the Outside Gate, but there are rare & risky but valid exceptions, such as when taking someone down with a 2-on-1 control of their arm, especially when they have an edged weapon in that hand.