This achievement requires you to equip the Engineer kit (Shotgun, Rocket, etc...) and kill ten enemies in a row without dying. The best method I can suggest for this is playing Conquest mode and laying a land mine at the base of a flag and run away.When someone starts to take the flag, shoot a rocket the flag and the mine will blow. Rinse and repeat.
This is a very hard achievement to win.
The shotgun at point blank range is a one-hit-kill, but the reload seems like it takes ages when involved in a multiperson skirmish. Stay low, move slow, and use all of your weapons to your advantage.
Now there is the 'exploit' of quick reloading, which can turn your shotgun into a pretty lethal close quarters weapon especially around multiple enemies. In the spirit of keeping TA a legit site however, I recommend you learn how to do that somewhere else.