How is a lop sao switch drill performed? I want to know the jut sao drill. I am told their are five?
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Sifu Michael McIlwrath who teaches Wing Chun privately in New York and New Jersey https://www.facebook.com/SifuMcIlwrath
 replies:

The Lop Sao drill varies from teacher to teacher, but I will list the 3 basic ones-.

1. Side A throws a punch to the face of side B. Side B uses Bong Sao to wedge his way in. Then side B using his other hand and lop’s side A punch but before he can do that side A cross grabs B’s hand and lop Sao him.

2. Side A throws a punch to the face of side, B uses Bong Sao to wedge his way in. While B is in Bong Sao side A juts with his punching hand on B’s Bong Sao and punches with his other hand forcing B to use his other Bong Sao. An alt, to this is instead of using the Jut Sao use Gum Sao in it’s place.

3. Side A throws a punch to the face of side B. B then uses Bong Sao to wedge his way in. Side B does not respond in time to Lop Sao,so side A with his punch on top of B’s Bong Sao bridges B’s Bong Sao an Wu Sao with the same hand and lop’s and grabs side B wu sao.