With a few teammates
With one friend
In a large area with lots of hiding spots
In a large open area
In an area with lots of cover
In a building
You pop out of cover and give him a round to the chest.
You sprint up on him and unload on him.
You wait until he passes then shoot him once in the back.
You wait until he is close, then pop out and shoot him.
You signal your team to open fire.
A Sniper Rifle
A High Capasity AEG
Here's an interesting quiz for you.