Takedown is a Stealth Perk in Kingdom Come: Deliverance. Let's you knock people out from a crouching position.
Not sure if this is a glitch or intended, but you will unlearn the Takedown skill when you drink the Lethean(?) Water potion.
Seems to only work if the target didn't see you. Also, sometimes it doesn't work even if you sneaked up on the target. Might be probabilistic.