Gyaku-tsuki, the reverse punch, is the most commonly used karate technique. Reverse punches are thrown with the trailing hand, like a boxer’s cross punch, but without crossing the centerline.
To throw a reverse punch, run your arm along the trailing side of your body, until your elbow is one fist-width away from your chest (like the starting point for a front-foot punch.) Then turn the fist over with a snapping motion, just like in front-foot punch. Remember to incorporate reciprocal action when punching by pulling the non-punching opposite-side hand to your hip, or performing a Kūsankū movement by pulling your leading-side hand across your centerline to the side of the face to swat an opponent’s counterattack aside.
[video of reverse punch from the front and from the side, blocking face with other hand]
Remember, punching power is generated by the wrist’s snapping turn-over, by tensing all of the arm muscles at the moment of impact. Any technique without snap is just a push.
[video of a side view of a series of reverse punches, hitting a kicking shield. The first three are arm-only, with no turn over. The next three are 6” punches. The next three are full-power reverse punches. Make it dramatic.]