Check out DK YOO’s explanation of the flicker jab:
I definitely recommend checking out some of DK YOO’s other videos. How he moves his body is incredibly impressive.
I also recommend studying Floyd Mayweather for this. He usually keeps his fist at his waist, and then punches just like a whip. The fist starts down low, and then gathers momentum in an upward trajectory and is “flicked” at an opponent. Because of the snapping motion, your fist is automatically in position after being thrown to throw a second or third punch with out much effort. Though you usually see professionals only throwing them one at a time. It’s also difficult to know where it’s coming from because the fist is kept low.
This jab is very useful in creating psychological damage because you can throw a lot very quickly. The punch starts from your shoulder, is thrown from your elbow, and then finished by squeezing your fist at the point of impact while simultaneously completing the full extension of your shoulder. This is very difficult to practice in slow motion, just like how it is very difficult to crack a whip slowly. The punch is meant to be a highly repeatable small explosion with the weight of your elbow and shoulder behind it. It is perfect for double jabbing, or even quadruple jabbing because when you bring your fist back after the initial jab, you don’t bring it all the way back to guard. You only bring it back half-way, because that’s all the distance you need after the initial jab. It isn’t as powerful as a straight or a hook, but the flicker jab can block your opponents’ vision which can set you up nicely for a chopping left or right.