From the moment you saw Asav you probably wanted to beat him up. He's not a nice guy, and that just might be why he's one of the main villains in Uncharted: The Lost Legacy.
You'll eventually have an opportunity to face Asav. Although you might be giddy to jump into the fight, you should approach with caution. Asav is a tough adversary, and certainly not one you want to take lightly.
When facing Asav, you'll want to prioritize dodging by tapping circle. Every few moments he'll look away, at which point you can jump in for a strike with the square button. Effectively, any time he's distracted you can pounce on him. Due to this, the battle comes down to timing more than anything.
Repeat this strategy until Asav submits to your power. Good luck out there!