Technically, the punch transition is any 2 footed landing followed by a 2 footed takeoff. Its that simple. More commonly, punches are recognized as the powerful stomp into the floor with an instant rebound that we’re so familiar with from gymnastics tumbling.
The key to this transition, as with all unified transitions, is the center of balance, and ideally, finishing early enough in the first trick to intentionally stomp down hard into the second. In order to punch straight up, the body must be centered above the feet. If the chest and hips are in front of, or behind, the feet, in relation to your momentum, the punch will create greater degrees of travel and flip. This transition is all about angles and timing.
How trickers utilize this transition a little differently is by transitioning from inverts into a vert via the punch. In order to do so, generally the feet touch with the chest a little bit low, but as they rebound, the retained momentum of the flip causes the body to straighten out and become vertical. Because of this phenomenon, it is not uncommon to see intended vert kicks from a punch transition turn into arguably inverted tricks by flipping at or near the horizontal plane.