Call of Duty: Modern Warfare 2
51 Achievements
27-33h
Unnecessary Roughness
Use a riot shield to beat down an enemy in Single Player or Special Ops.
34.5%
How to unlock the Unnecessary Roughness achievement in Call of Duty: Modern Warfare 2 - Definitive Guide
A riot shield is a new defensive weapon in MW2, it basically blocks bullets and you can hit people with it, you need to hit somebody twice with the riot shield to kill them and therefore unlock the trophy. There's few places in the campaign with riot shields, but the first time you will encounter one is during the mission 'No Russian', when you're escaping from the terminal there's lots of police with riot shields, just kill one of them, take their riot shield and then bash somebody with until they die, trophy will pop shortly afterwards.
If you have the setting to disable this mission, you can also do it during the mission 'The gulag' when your in the armoury and also there's a few spec ops missions that include riot shields. Video by Nextgentactics:
https://www.youtube.com/watch?v=x-8tCxcQZkA
An easy place to get this is on the mission The Gulag in the campaign. Towards the middle of the mission, you are forced to pick up a riot shield. Crouch to make sure you won't get shot and then walk towards an enemy. Once you are close, click the to beat them down. It only takes one hit to kill them.
You can also pick a riot shield up and kill an enemy in No Russian (the optional mission in the campaign) and then Special Ops missions Breach and Clear and Terminal.