Dying Light

To get this you must have:

(a) a two handed weapon, such as a sledgehammer and
(b) the Ground Pound (under the Power skill tree) skill

So what you do is:

1) Go find a bunch of infected clustering around a bus. I went to Infamy Bridge over on the far right of the map because it's crawling with infected and you have to get to the bridge for this:



2) Hop on top of the bus
3) Throw down a firecracker to get the infected to bunch up.
4) When they are clustered, face the infected,
5) Press to jump and as you are mid way down hold . You'll know you're starting a ground pound because motion slows down.
6) Now turn around and go back to step 2

Here's a video... http://1drv.ms/15JkUdE

If you want to get this as soon as possible then go with SneakyStabbalots guide. You can unlock the Ground Pound ability in the Power Tree at level 7. However if you have patience and wait to Power level 10, you can unlock Drop Attack which also works for this achievement and in my opinion is more reliable, easier and fun.

The problem I found with Ground Pound is it took too long to set up. You have to get a group of people together and find somewhere high enough to jump from and go through the animation. And then a lot of the times the enemies would only get stunned. Never mind finding a reliable 2 handed weapon.

Using the Drop attack you can just simply run around the town with a more nimble one handed weapon, and every time you jump hold as you land and as long as there is a zombie where you are landing you will get a kill every time. This will come along very quickly and you will not need to go anywhere out of your way.