You need a friend to grab this achievement in Halo: Reach, formally called Workers’ Compensation. You need to run over an enemy with a forklift, but it does not work with traditional enemies. The best way to make it happen is in a custom Firefight match.
You or your friend need to host the Firefight match and then go to the options. You want to go through the Elite Settings and Spartan Settings, highlight the Base Traits option. Click the Shield and Health Option, switching the Shield Multiplier to No Shields. This way, the Elites and Spartans in the game have no shields during combat, and to turn the health down.
Next, pick the Courtyard map. This location has the quickest to find forklifts.
When you have the map and shield options adequately adjusted, make sure your friend is a Spartan or an Elite, and then you’re the opposite of them. After that, launch the game on the easiest difficulty.
From there, you want to find the forklift on the map. The first one is on the left side to where the Spartans spawn into the game. It’s hidden behind a large metal crate, but not too hard to find. After that, you or your friend need to hop into and then run the other over. The person who performs the kill receives the achievement, and then the person who dies needs to respawn and do the same thing.
You do not need to do the achievement on this map, but the Courtyard has the most obvious ones to find. There are two on the map, one on the left side and one on the right.