Tom Clancy's Splinter Cell: Chaos Theory HD
37 Achievements
15-20h
PS3
Knock, Knock-out
Knock out 5 guards by bashing doors
7.0%
How to unlock the Knock, Knock-out achievement in Tom Clancy's Splinter Cell: Chaos Theory HD - Definitive Guide
Malak101
Pick a level you are familiar with, get behind a door and use whistle 
to lure a guard you can see towards the door. Press 
and select “Bash door” to knock the guard out.