A knockout, often referred to as blackjacking, refers to removing an enemy from gameplay without killing it. This is a very important move in Thief, as hard and expert difficulties typically disallow the player from killing anyone. This can be accomplished with the blackjack, Gas Arrows, or Gas Mines. Certain enemies such as Fire Elementals and Zombies, however, cannot be knocked out at all. Some very weak characters, such as Servants, may accidentally be killed from an attack intended to knock them out.
How to accomplish a knockoutEdit
The blackjack is the primary weapon for knocking out enemies. On most enemies, it can only be used when they are not alerted to Garretts presence. Depending on how alert the enemy is, it may also accomplish a knockout if they are searching for Garrett.
In Thief I and IIEdit
In the first two games, the blackjack works from most angles and simply needs to connect with the opponent while they cannot see Garrett (save the "Surprise" type mentioned below). This includes when they have been blinded by a Flash Bomb or when Garrett is using an Invisibility Potion. Unarmed civilians can be knocked out no matter how aware they are.
The Airborne knockout is a 'secret' knockout move. Garrett just has to swing, and then jump. If the blackjack makes contract and the NPC knocked out, then it will be considered an Airborne Knockout, and are even tallied in the stats screen after the completion of the mission.
If a hostile is searching for Garrett, or a hostile can only be taken out from the front, Garrett can lean forward and swing the blackjack (providing he is in a good shadow).
Hostiles have a split second to react to Garrett's presence. In this time, they can still be knocked out, but it requires the player to be very quick. If they have finished their exclamation, it will be too late.
In Thief: Deadly ShadowsEdit
In the third game, the mechanics of the blackjack changed considerably. Enemies and civilians cannot be blackjacked once alerted in any way, and Flash Bombs do not allow a knockout either. Blackjacking is significantly more difficult to accomplish.
Instead, the blackjack will only work by a proper "sneak attack." Garrett must be behind an completely unaware enemy and the player must wait for Garrett to raise his arm over his head (indicating he is in the right position). Pressing the attack button while Garrett's arm is readied initiates a scripted knockout animation, rendering the opponent unconscious and causing them to drop everything they were carrying, including their weapon.
Gas Arrows and MinesEdit
Gas Arrows and mines emit a type of knockout gas which is effective even on fully alerted enemies and can affect multiple enemies at once if they are close enough to the cloud of gas.