One of the most improper technique being used in the Wing Chun system is the Bong Sao. You’ll see it in movies or even in YouTube, where the person will use the Bong Sao as a technique to deflect or counter an incoming punch. It may look nice, but it is a highly ineffective and improper way to use it. In Wing Chun, Bong Sao has a nickname, which is called the Losing Hand (敗勢手). Meaning you only use this technique when you’re about to lose your structure. In order to protect yourself from losing balance and structure, you’ll need to use the Bong Sao. For example, when your hand is forcefully being pulled down or pulled toward the person and if you don’t use Bong Sao your opponent will make you lose your entire body structure.
If you’re planning on use Bong Sao for the purpose of deflecting or counter an incoming punch it will absolutely fail, especially if the person rushes in with the punch. There won’t be enough time to intercept the punch with the Bong Sao and to make things worst you’re allowing the person’s punch to be on top of your arm. With the upward movement of the Bong Sao, you’re only guiding the person’s punch to your face. Even if you shift your body in an angle, now you’re in position where your other arm is too far to defend or even counter the second or third punch, which comes in very quickly especially from a boxer.
Using the Bong Sao to deflect from a punch is also unrealistic. Why is it unrealistic? One of the worst thing you can do in a real confrontation is to premeditate or anticipate a person’s attack. There are so many factors to consider when an attack comes (the speed, height of the person, distance, power, body position). When a person comes in, how do you even know it will be real straight punch? It could even be a fake punch to led to a hook or a fake jab to go with a cross punch. When a situation like this happens you should only rely on techniques that will give you the upper hand, where you can change into a better position, to stop him from moving or from throwing a 2nd or 3rd punch. But by purely relying on Bong Sao and “thinking” he will throw a straight punch at you will put you in grave danger. As it was mentioned before, Bong Sao isn’t even a good technique to stop a straight punch in the first place.