The Wing Chun Punch
Because of the emphasis on the center line, the vertical fist straight punch is the most common strike in Wing Chun. However, the principle of simultaneous attack and defence suggests that all movements in the Siu Nim Tau with a forward execution flow into a strike if no effective resistance is met, without need for recomposure. Other explicit examples of punches can be found in the Chum Kiu and Bil Jee forms, articulating an uppercut and hook punch respectively.
The vertical punch is the most basic and fundamental in Wing Chun and is usually thrown with the elbow down and in front of the body. Depending on the lineage, the fist is held anywhere from vertical to horizontal (palm side up). The contact points also vary from the top two knuckles, to the middle two knuckles, to the bottom three knuckles. In some lineages of Wing Chun, the fist is swivelled at the wrist on point of impact so that the bottom three knuckles are thrust forward adding power to the punch while it is at maximum extension.
The punches may be thrown in quick succession in a 'straight blast' or 'chain punching'. When executed correctly, it can be used as a disorienting finisher but is often criticised for encouraging weaker punches that don't utilise the whole body.
Wing Chun favours the vertical punch for the following reasons:
Directness. The punch is not "loaded" by pulling the elbow behind the body. The punch travels straight towards the target from the guard position (hands are held in front of the chest).
Protection. The elbow is kept low to cover the front midsection of the body. It is more difficult for an opponent to execute an elbow lock/break when the elbow occupies this position. This aids in generating power by use of the entire body structure rather than only the arm to strike.
Strength and Impact. Wing Chun practitioners believe that because the elbow is behind the fist during the strike, it is thereby supported by the strength of the entire arm rather than just a swinging fist, and therefore has more impact. A common analogy is a baseball bat being swung at someone's head (a round-house punch), as opposed to the butt end of the bat being thrust forward into the opponent's face (wing chun punch), which would cause far more damage than a glancing hit and isn't as easy to evade. Many skilled practitioners pride themselves on being able to generate "short power" or large amount of power in a short space. A common demonstration of this is the "one-inch punch," a punch that starts only an inch away from the target yet delivers an explosive amount of force.
Alignment & Structure. Because of Wing Chun's usage of stance, the vertical punch is thus more suitable. The limb directly in front of the chest, elbow down, vertical nature of the punch allows a practitioner to absorb the rebound of the punch by directing it through the elbows and into the stance. This is a desirable trait to a Wing Chun practitioner, where in contrast the rebound of a horizontal, elbow-out punch promotes torque in the puncher's body. This is because the limb and elbow are now directing rebound force outwards instead of inwards due to the positioning of the hinge-structured elbow. This aids in generating power by promoting use of the entire body structure rather than only the arm to strike. This can be easily demonstrated; hold your fist vertically, in front of you, your elbow pointing down, one foot behind the other. Make sure your elbow is in your centerline. Then ask a friend to push into your fist while you attempt to resist. You will feel the push pressuring your legs and stance. Repeat with a horizontal fist, elbow at shoulder height and to the side. You will feel the incoming push twisting you sideways.