This achievement is story related, just continue playing to unlock.
*** Spoiler - click to reveal ***At some point in the game you have to go rescue Dr. Zere, which is taken by Rais' men. You end up in a parking garage where you'll be knocked out. You wake up in a large arena with an empty inventory, so use the environment wisely to kill the 3 containers filled with infected, e.g. by kicking/grappling them into spikes. There are a few items available on the ground and on top of the containers that can be used as weapons; use your survivor instinct to find them.
An addition to this solution (thanks to THE Mr Fill):
Get the Survivor skill Camouflage Attack (level 12), so you can try to pull one away from the crowd, kill it, then use their blood to camouflage yourself & walk around killing them. To make it even easier get the Power skill Takedown (level 13), together with Camouflage Attack you can walk through a crowd snapping necks & not weakening your weapons.
When you're done dealing with the infected, Rais tells you to pick up a machete and brings in a boss zombie, a demolisher. The machete should be used on the back of the demolisher, frontal attacks and attacks with distant weapons are not effective. Watch out for the rocks that are thrown at you. Frequently use dash (press , or with ) to prevent taking damage and attack the demolisher when he turns his back on you. Be careful, as there will spawn some other infected from time to time, so take a look at your map regularly.
Once you have beaten the demolisher, a nice cut scene will start. Eventually, you will try to escape. From the moment you can take control again, start running. Use the tunnels to prevent being shot. In the end, you have to make it to the top of the building. Just keep moving and you will be safe. Return to the marked safe zone to report back to Brecken. After this cut scene, the achievement will pop.