This is a story-related achievement and cannot be missed. It will unlock upon defeating Hazmat "Jimmy", the boss at the end of the Prologue.
Later into the Prologue while searching for Nick you will come to a gate leading to San Romero High School. A crew of zombies will attack you, one by the name of 'George', kill them. Afterward, three zombies in Hazmat suits will attack you. The leader will have a health bar with the name 'Jimmy'. Watch out for the explosive tank that "Jimmy" will throw at you once he's health is low. Try to dodge them as good as you can!
Once you defeat all three zombies you will get this achievement.
A video solution by GameGuideCentral.com, credits to them: