The Drop
Sometimes an attacker is able to catch a foe off-guard and gets “The Drop” on him. The GM decides when this is in effect—usually it’s when the victim is bound or completely unaware of an attack. The Drop usually happens up close but the GM can also allow it in other situations as she sees fit (a sniper attacking an unaware and stationary target).
The Drop adds +4 to a character’s attack and damage rolls against that target for one action.
Knockout Blow: If a character takes enough damage to be Shaken or worse from an attacker with The Drop on him, he must make a Vigor roll (at −2 if the attack was to the head) or be knocked unconscious.
KO’ed characters stay that way for about half an hour or until the GM decides it’s dramatically appropriate to wake up. Note that Knockout Blows come from any kind of damage, not just blows to the head!