The bong sao is a bent arm deflection or parry from Wing Chun. The bent arm is similar to that found in age uke, as well as harai otoshi uke, but is applied differently.
It involves making contact as the punch extends, but instead of knocking it away, the bong sao continues into position by moving the hand forward and rotating the elbow of the blocking arm upward and toward the opponent as it extends. The deflection is a natural result of the extension, and the punch is deflected when it slides along the forearm.
As shown by Ip Chun in the cover image, the opposite, non-blocking arm is usually used in a mirror image. It often blocks as well, either in an inward or outward parry with the palm or wrist. Do not use force. This is not a snapping block, or one to knock away the attacking arm.
The idea is simply to not be hit, and to be in a position to immediately counter, if one is not already set in motion by the block itself.
When bong sao is used to deflect a same-side hook to the head, the opposing hand will often come to protect the side of face as well, so the bong sao becomes part of a double block.
There are many ways to apply bong sao. Variations depend on the situation and fighting style of the user.
Practice with it in various ways. Then try age uke as a bong sao deflection (hand slicing forward and up as the elbow raises). The blocking hand probably will end up somewhat farther forward than the normal one fist distance off the forehead. This is to be expected, since all techniques will vary somewhat in application from how taught.
Here’s another video on variations in application of bong sao.
It works on kicks, too.
Here bong sao is used to block kicks. The inside deviation he discusses is bong sao.
Also note that using the leg to block can be painful. Body conditioning may be required to give and absorb the resulting punishment.
We recommend working with bong sao for yourself. When you can get a training partner, chi sao practice will help.
We’ll work on that in a future lesson.