Isle of Conquest All-Star

Kill a player : don't even need to be a killing blow.

Assault a base : Just cap something.
Tip : Oil and quarry are often left alone.

Destroy a vehicle : Hope the other team will cap one of the 2 shop.
Tip : You can camp the shipyard and destroy a catapult(25k health) when it spawn. You need killing blow.

Defend a base : Need to wait till someone try to cap one of your base and recap it.
Tip : Most tricky one. Again you can wait at oil or quarry for someone, let him steal it and cap it back before they get it.
What I did for mine was waiting near the oil factory with a catapult, wait till someone go cap it. Most of the time the person will just run away while it cap. You can just throw yourself and cap it back or simply throw, kill the person and cap.

Good luck!

Note that this achievement is not required for the Isle of Conquest meta, so you don't need to do it if you just want the tabard.

Armory is showing the progress of this achievement being completed over and over again, even if you are killing players in the world. Along with achievements like 'Troll Slayer', etc.