a right hook

A “hook” is a kind of punch in boxing. When a boxer does a "hook", they swing one arm in a circular motion from the side. A "right hook" is done with the right hand.

a devastating (punch)

Something that causes a lot of harm can be called "devastating". You can use it to talk about a battle or attack in war:

The Battle of Galipoli was devastating for the Allies.

You can also call a punch or other blow "devastating" in a fight between two people:

Oh, that kick was absolutely devastating!

One other way that we use "devastating" is to talk about something that caused emotional harm:

My dad passing away so suddenly was just completely devastating. It took me years to process it.

catch (someone) with a (punch, kick, etc.)

In a fight, the fighters try to avoid getting hit. So when one fighter manages to hit the other one, you can talk about it like this:

She caught her with a spinning back kick.

You can also say "get caught with ___":

If you don't keep your hands up, you're going to get caught with a punch to the face!

knock (someone) out

This means to hit someone on the head very hard, making them go unconscious.

I skiied right into a tree branch and it knocked me out.

You can add “cold” at the end to emphasize that the person was completely unconscious and not moving:

She knocked him out cold!