Eight Dragons (US)

The sledgehammer is a powerful melee weapon that will spawn on various maps. Simply press B to crouch and pick it up, and then A to attack someone to knock them out and unlock the achievement

Fun Fact: this is a reference to the hilarious late 1980s television show Sledge Hammer, where the shoot first ask questions later lead character would always say "Trust me, I know what I'm doing!" before doing something very stupid.