To condense it for you, punching power, specifically a straight punch which I assume you’re trying to animate would derive from the force being used to propel forward / lunge from a standing position and also from pivoting or twisting the body slightly.

If properly connected then the punch becomes powerful and effective.

To animate this you should set things up with a base that can stretch and have this base be in a starting position, a standard boxing stance should do the trick and is the best for animating to keep things easy and simple.

Keeping in mind what you know try and work with ‘perspective’ and stretch the base to make it appear twisting and propelling off from the ground forward.

A straight is usually meant to be delivered with more power than say a jab which is more of a fast flick or whipping action of the opposing dominant hand. Still aim to make it fast though but keep in mind the heavier an opponent the slower they will punch but ultimately with more force then a faster lighter one, hence the terms of ‘Heavyweight’ (200lb range) and lightweight (130lb range).