Okay, so wu sau is another fundamental technique in Wing Chun. In Cantonese, wu sau basically means "guarding hand" or "protecting hand." Generally in our pre-fighting position or our engarde position like I explained before, it' your backup hand. However, when you're using it in your engarde position, your wu sau is generally much more relaxed. So, like I explained before, it's in a ready position to punch forward. However when you use wu sau at close range in chi sau or with a partner, or certainly when you practice in the form, the wu sau is completely articulated and is standing totally upright like this. And the reason is that you need the complete surface area here in order to defend attacks at close range.
When you're at distance, you opponent is far away from you, it is not critical or necessary for you to have your wu sau cranked all the way up, it can be much more relaxed, but when we're actually engaged with our opponent we need to do it a little bit differently. So this is how a wu sau would function for example in a chi sau. If I were to give, from whatever position I'm at, I want to give my opponent a pak sau punch, one of the most standard defenses is to use bong sau wu sau like this here. Okay? Now if his wu sau is upright like this and it's right in the center, he creates a wedge, whereas if I were to punch this way here, even if I try to go to him without using a lot of force, he can basically wedge my punch off.
But if he just changes it a little bit where he doesn't fully articulate the wu sau, in other words he gives me a lazy wu sau, I can slip in like this, because there is an open space here for me to hit him. If he fully articulates the wu sau as I come in, now he has a better defensive angle. Of course, the warning is, you don't want to make your wu sau too stiff or too rigid, because if I run into it and he's just too strong, I'm going to change it and use that against him. So wu sau still needs to be elastic, it still needs to be relaxed, but you need to make sure that you have a fully articulated wu sau because this one simply won't work at close range to defend.