In my opinion this is the hardest achievement in the game but you can get this with hard work. First of all you got to understand the 3 main combat techniques shove, punch and block. Use all these techniques wisely and also use bows every chance you get. When you get around 13 kills you will face 2 bad guys and this is where you need to find a gun. Once you get a gun use it when you have 2 or more bad guys.
When fighting archers i was usually selling stuff because they don't come close to me
Also throw weapons you are not using close to the selling machine so you can quick sell them.
Keep moving is what i kept doing you don't want to get surrounded.
Lastly at the start of each round sit it the middle or in a corner so you can double check how many or what type of enemies you are up against.
Just keep trying this is obtainable with patience.
Thank you to gobey17 for helping me with tips on this one.
Good luck everyone :)