Ok, it's best never to have to throw a punch/strike because like a bullet leaving the barrel, you can never really be sure how it will end. Too many times, people get into stupid social matches over things like parking spaces or a perceived slight and when they strike, they never expected the other person to hit their head on the concrete--and die.
But if you are going to punch/strike, the situation should justify the action. Make it count (at that point, his hitting his head on the concrete is a bonus). In a perfect punching/striking world we want to step through or past our antagonist, bend the forward knee and keep the spine straight and the back foot flat. This will allow you to bring your body weight to bear in the strike. This is what allows a 90-lb woman to drop a 225-lb man.