There's a Ranger in one of the 1st floor hotel rooms in NoVac who teaches you a combat perk if you pass a speech check to make him feel better about himself. It says you should execute a power maneuver while backing up, or something like that. I have no idea what its talking about, I thought h2h was just trying to figure out how to block and punch effectively (which I can't, so I carry guns.)

Holding down left click while backing up. You might need a certain Unarmed skill to do it.

I haven't been able to figure it out either, my unarmed is still 17 cus I'm a gun user as well so maybe that's it (but then it doesn't make sense for him to even teach it to you).

I have noticed there are some moves my guy will do ie- with a knife chasing someone and doing a power strike he leapt at them and it did a killcam kill

Whats a power strike?

I got the move from the guy and can do it perfectly fine and my unarmed skill is really low. All you have to do is hold the left stick while going back its not that hard.

A power strike is when you hold down the attack button for a second or two (and your unarmed) and your character punches harder. So to do the ranger takedown you need to hold the attack button and backup as you hit the target. It can take a few tries to get good at it but its helpful once you figure it out