A backstab is a context-sensitive attack that a Spy can perform with any of his melee weapons. When a Spy uses any one of his knives to hit an enemy from behind, a successful backstab is performed, resulting in an instant kill in almost all cases.
A Spy may backstab an enemy as long as the enemy is close within standard melee attack range, and the Spy is within a 180° range behind the enemy. Backstabs deal damage equal to 200% of the target's current health and always deal critical hits (increasing the damage to 600% of the target's current health), unless otherwise prevented by a Battalion's Backup. However, a Battalion's Backup will not cause a damage reduction. Due to the mechanics of the Spy's melees, unlike most melee weapons, backstabs connect instantly upon activation; there is no delay between the moment the player attacks and the moment the backstab is executed. To indicate that a Spy is within the required range to perform a backstab, he will raise his knife then turn it downward, primed for a kill. The knife will remain in this position until the target is no longer in reach, or the Spy attempts a backstab by attacking. The knife also turns downward if positioned behind a disguised or Cloaked enemy Spy. When the knife is pointed downward, the Spy simply needs to attack for an instant kill to occur.
A backstab can be performed while the Spy has a disguise active, although the disguise will be removed upon attacking, regardless of whether or not the attack connects with the enemy. A backstab cannot kill a Scout made invulnerable with Bonk! Atomic Punch, a player who is under the effects of an ÜberCharge, or a Spy with the Dead Ringer active who has more than 3 health points. The Razorback, an unlockable secondary weapon usable by the Sniper class, blocks a single backstab attempt. The Razorback also causes a temporary (about 2 seconds) inability to attack, Cloak, or switch weapons for the offending Spy. Thus, the Razorback makes Snipers less prone to backstabs and encourages Spies to use their secondary weapon instead.
Backstabbing with Your Eternal Reward or the Wanga Prick causes silent death. Your victims will not scream, their body will vanish, and no killfeed notification is given to the victim's teammates. The attacking Spy will disguise as the fallen enemy almost instantly.
Backstabbing with the Big Earner will fill the Spy's Cloak meter by 30%, regardless of which cloaking device is equipped.
Backstabbing with the Spy-cicle, like Your Eternal Reward, also causes silent death. It also does not alert the enemy team's killfeed. However, instead of cloaking the corpse, they will turn into an ice statue. This is a clear sign that there is a Spy in the area, and other enemies can use this to track you down.
Backstabbing a giant in Mann vs. Machine will deal up to 750 base damage, but this is reduced to 25% of that (188) by default; each armor penetration upgrade restores 25% of the base damage, up to 125% of the base (938).
- Stab-and-Sap: Stab a (turtling) Engineer, before switching to your Sapper and sapping the Engineer’s Sentry Gun; this must be done fast enough that the Sentry Gun doesn't have time to turn around and kill you. An experienced Spy may track the Sentry Gun's turning direction and move against it after he stabs (as it will follow him, this will buy him more time). Using Your Eternal Reward can be useful in this approach, as you instantly disguise upon a successful backstab, preventing the Sentry Gun from detecting you and retaliating; a Spy without a prior disguise must rely on cover to avoid the Sentry Gun's attention, as the Sentry will not be fooled by your instant disguise once it has already begun firing. This tactic is slightly easier on Engineers using the Wrangler, because the Sentry Gun is disabled for one second after the Engineer's death.
- Sap-and-stab: Sap an Engineer's unattended building as bait, hide, then stab him when he returns to remove the Sapper.
- Overhead stab or Stairstab: Stand at the top of a set of stairs, ramp, prop, or any slight elevation, facing down at an enemy approaching you. Run forward and crouch-jump, releasing forward while turning in mid-air to stab them in the back. This technique can be difficult to master, but it is also difficult to protect against, as the enemy has to turn almost completely around to avoid it. The amount of time spent crouching is critical for this trick; the stab will not register without crouching.
- More experienced players will either avoid climbing, moving towards you, or even backing out of range when they see a Spy at the top of the stairs or ramp. Instead of advertising your intent, you can perform the stab without having to wait at the top. While retreating up the stairs, jump up and hold back. Most players will continue to run forward, passing underneath you. Backstab them as you land.
- Some Spies may prefer to execute this stab by landing on top of the enemy's head instead of directly behind them. To do this, you will have to stop yourself in the air to avoid sliding off the player's head by using the opposite strafe key than the direction you are going. You can then stab while crouched on top of the other players head. The benefits of doing it this way is that it can be executed a lot faster, so the other player has less time to react, you have more time to stab, and even if the player turns completely around, you can still use your strafe keys to position yourself into their backstab hitbox and get the stab.
- Quickstab: While an enemy is running towards you, let them run past you before spinning and stabbing their retreating back. This is one of the only reliable methods of backstabbing Scouts or any enemy that buys your disguise.
- The Corner Stab: This is an advanced Spy technique. The technique involves luring an enemy to a corner, then immediately backing out and stabbing the enemy as he turns in the way you did. Note that this can sometimes only work once or twice on an enemy, and is best used on pursuits with Scouts or Pyros.
- The Topstab: Sometimes Engineers will place their Sentry Gun and Dispenser in a fashion that allows the Engineer to have his back to a corner, making him seemingly protected from backstabs. It is possible to jump on this Engineer's head via climbing from his Dispenser or Sentry Gun while positioning yourself over the Engineer (facing the same direction as him) around his back until you get the "Knife-raised" animation, allowing you to score a backstab with a click.
- The Leap Stab (or Eagle Stab): This is similar to overhead stabs, but instead it focuses on striking enemies from a significant height (usually from ground above the opponent - bridges, roofs, ledges) and is best used with either the Cloak and Dagger or Dead Ringer. Cloak on a bridge/high place (or hide if you're using Dead Ringer) and as the enemy passes beneath the spot, jump after them and stab them in the back. Doing the stab itself is easier with the Cloak and Dagger, but getting away is easier with the Dead Ringer (especially against multiple opponents). The enemy will have no idea where you came from, as they usually do not check the skies.
- Attempting to leap stab the same opponent at the exact same spot twice could be a bad idea (doing it again elsewhere is more secure, though he might be paranoid) - this tactic may be best used while the enemy is distracted, as they will not notice you jumping on them.
- The Matador stab: This is an advanced Spy technique and a difficult one to master. To perform it, you must be facing a single enemy, who is facing you. Either run towards him or let him approach you, then, just before he is in melee reach, strafe in one direction (left or right) for a split second, before quickly changing direction and strafing to the opposite side. This will reveal the enemy's back for a very short moment as he follows your first strafe, and you should stab him promptly during this brief gap. This is useful for those players that dismiss Spies and try to melee them, such as some Scout players. Should this technique fail, and you miss the stab, you will be extremely vulnerable in close-range and will almost certainly die, but when performed correctly, this technique enables you to stab an enemy in a potentially fatal situation. Great for Dead Ringer Spies. Not recommended to try this on Pyros; the technique might still work, but unless the Pyro wants to melee you, you will probably be set alight and dealt a fair share of damage. Once you get more confident with this stab, it becomes perfect for Pyros who try and come at you with their Axtinguisher. One quick side-step and you should have them.
- The Understab: This backstabbing technique involves hitting an enemy with the knife in a second that you are under them. It is typically used on pursuers of the Spy when the victim is falling from a height and the Spy can abuse this to strafe under the victim using the horizontal arrow keys and stab them for the brief moment the victim is exposed. The technique sometimes involves standing still before strafing to confuse an enemy and thereby generally forcing them to move in a predictible pattern and allow for an opportunity to get under the victim as they fall. The Understab is also known for being a risky counter to the above mentioned Overhead/Stairstab as the player is turning. The understab can also be used on unaware enemies in areas such as spawns where players drop from a height or other common paths that have drops that the Spy can use.
- The Strafe-and-Snap: This is a highly advanced backstab technique. This stab is similar to a matador stab, but instead of strafing back to the player, you strafe away. To execute this stab, run at the enemy, but just before you reach them, release the forward key, then as fast as you can, snap your view towards the player at the same time as strafing the opposite direction while clicking. This stab takes a lot of practice to master, but once you get it down, it can prove extremely useful for tight situations.
- Due to an in-game glitch, a stab that has appeared to have occurred from the front can sometimes be rendered as a backstab. Known more commonly as a facestab, these kills are now mostly the result of lag compensation by the game engine itself. Prior to many game patches, facestabs were more common due to bugs in the way the game detects a backstab. Facestabs take two forms: the "valid" stab and the "true" facestab. Most of what the recipient sees as a facestab is usually either a cornerstab or a sidestab, where on the Spy's screen, he sees it as attacking the target's back, but due to lag, the target sees the Spy attacking from the front. A valid facestab works as intended by the developers, making correct use of lag compensation. In a true facestab, the Spy appears to be attacking an enemy from the front on both players' screens, but lag compensation results in it being registered as a backstab. This is considered a bug.
- Another community-coined term is the failstab, which refers to a backstab which should have succeeded but instead did only normal Knife damage, despite the backstab animation playing fully and the Knife connecting. These stabs are almost always linked to the latency conditions between the server and the player.
- Rarely, during taunts, the player's 'back' changes position; it becomes directly behind the player's 3rd-person camera, which means that players can avoid backstabs by moving the camera away from the Spy. This generally occurs by accident; for example, when you position the camera in front of you to watch the taunt yourself, making your back into your front. Facestabs can also rarely occur this way.
- The angle required for a backstab is based on the direction the victim is looking; however, all players have models whose normal stance has their backs rotated to the left slightly, due to the way they carry their respective weapons (this is most prominent with Heavies). This means that at certain angles you appear to be stabbing your target in the back, when in fact you are not inside the 180 degree angle for backstabs. Equally, there are valid backstab positions which appear to have you stabbing slightly into the front of your victim. These hit-box positions can be determined by the shoulders of the character models.
- When a player for the opposing team is standing on top of the Spy, the Spy can always perform a successful backstab regardless as to whether or not the Spy's aim falls within the regular backstab radius.
- Originally, the Spy's backstab animation was just over a second long and manifested as the current animation, but was slowed down. This was changed to the current, sped up version used today in the interests of balance. Before this change, skilled Spies would "quick-stab". This involved staying out of backstab range of the victim, and then swinging the Knife just before entering backstab range, thereby bypassing the backstab animation but still rewarding an instant kill.
- Killing a player with a backstab will sometimes cause a special backstab death animation. This animation has a 25% chance of occurring, and varies from class to class. The Sniper performs this animation and sound during Meet the Spy.
- The Sniper's backstab animation was first seen in Trailer 2 before any backstab animations were integrated into the game.
- Despite dealing no damage, backstabbing an enemy who cannot be killed (Scout under the effects of Bonk! Atomic Punch, Übercharged enemies or Spies, cloaked with Dead Ringer) deals a great amount of knockback that can easily be used to push the enemy into environmental hazards, such as off the side of DeGroot Keep, causing him to die while invincible.
- When the server has Random Crits turned off "tf_weapon_criticals 0", the backstabbing animation is removed, resulting in only a swing instead of a stab while dealing only 200% of the enemy's health instead of the usual 600% with Random Crits turned on.