Very simple trophy. Full disclosure, you must be playing as a Soldier to unlock this trophy
Step 1: Reach level 5 (unlock action skill)
Step 2: Find enemies (skags outside Fyrestone are best)
Step 3: Use action skill (stay in front of the Soldier's turret)
Repeat steps 2 and 3 until you unlock the trophy. The Soldier is one of the easier characters to unlock this so it shouldn't take long.
Happy Hunting :)