I was recently talking with a friend of mine about Flag over on Facebook. He wanted to know how powerful the Black Flag was in comparison to other superheroes. He is roughly in the same power category as Captain America. But who he can beat depends on each character he faces. For example, it would be tough for him to beat Cap. But he could take the Hulk in one punch. Why? Because the Hulk can't fight. He's a rampaging monster, exactly the type of big muscled goon Flag has fought all his life.
The problem with guys like the Hulk is that they can't fight. They have no real ability to inflict pain, only damage and destruction. A good straight punch to the jaw on a creature the size of the Hulk will put him down for the count.
Moving onto the issue of KO. This is a much more elusive commodity than people think and ensuring that you achieve one is not always easy. The aim as you may know is to achieve "brain shake" whereby the brain, which is suspended in fluid in the skull is made to collide with the interior of the skull. This causes neural overload and KO results. The best way to bring about this state of affairs is to strike as near to the point of the jaw as possible without expending your power by sliding off. It should be noted that strikes from the side (hooks etc), to the jaw tend to make the opponent fall in the same direction as that from which the hit came. This may result in a head connecting nastily with a hard object such as the pavement. A harder but more skilled strike is over the top and down onto the jaw which can cause the opponent to virualy sit down, thus lestening the chance of subsidiary head injury.
Not my words, but I've studied this stuff and trust me, the guys in comics have relied on their powers so long, they've forgotten what real fighting is all about.