Laap Sau 擸手is one of the most effective hands in Wing Chun. Laap means grasp. In the forms Siu Lim Tao 小念頭and Tsum Kiu 尋橋 we do not use Laap Sau, but in Biu Ji 標指, near the end of the form, there is a Laap Sau technique. However, this needs explanation as it is not exactly what we see.
For a smaller and gentler person to grab a bigger and stronger person, whether with one hand or two, is useless. That is why in Wing Chun we do not hold so tightly. We usually grasp the opponent with only four fingers and do not use our thumb. The thumb stays closed alongside the fingers when we grasp the arm for instance, not underneath the arm. This means that if the opponent pulls back we can easily let go and we will not be affected by his strength and so we are still safe.
Why do we grasp our opponent’s hand? We do this when they use their strength but only for a very short time to move them a little while we hit them with the other hand. Also sometimes we grasp them to confuse an opponent or to see how they will react. If they lose their focus, then we can hit them with the other hand.
If we ever do grasp an opponent using the thumb underneath their arm or wrist, it is because in this situation we want to make them lose their balance. So we must know how to use Laap Sau well in different ways to suit the situation.