"In fantasy, heroes get knocked out, awaken after a while as if from a nap, and plunge right back into action. The truth is, a mild concussion is disabling for periods ranging from hours to days, and as for a severe one, the consequences are not pleasant to watch."

— Poul Anderson, "On Thud and Blunder"

In fiction, anyone caught unaware may be easily, instantaneously and noiselessly incapacitated with a single blow to the head (or alternatively, a karate chop to the neck). A character thus treated will usually be perfectly fine afterwards; oh, they may have a headache, dizziness, slightly blurred vision, or in the very worst cases, Laser-Guided Amnesia, but this is nothing compared to the real danger — the Bad Guys standing around the operating table (or other heavy piece of furniture) to which they find themselves tied down.

For heroes, this is the perfect way to dispatch the villains. When you bonk someone on the head, you don't have to worry about breaking any moral codes or violating the censors on weapons, guns and blood. In other words, when fictional characters take a blow to the head, they'll suffer nothing worse than an unplanned nap. (This is why In the Back does not apply — hitting someone from behind is not really dangerous.)

For obvious reasons, this is not Truth in Television. The brain is a complex and notoriously fragile organ, and even minor trauma can have profound or devastating results. It's the difference between turning a computer off by shutting it down and by hitting it. The latter is likely to cause serious long-term damage.

Most real-life unconsciousness due to injury lasts only a few seconds, not some indeterminate amount of time lasting hours or days during which our hero can be carted around, dressed/undressed etc. To hit someone on the head hard enough to make them unconscious for an extended amount of time requires a fair bit of force, and such an impact is going to leave visible damage to the head. If you are out longer than a few minutes, some combination of brain damage, coma, cranial bleeding, loss of motor and cognitive functions, and amnesia is more than likely to greet you when you wake up — if you wake up. That is not to say people never get knocked unconscious for an extended time and wake up without any lasting damage, but it is the exception rather than the rule, and there is no reliable way to safely intentionally do this to someone. Indeed, fully reliable and safe ways to nonlethally incapacitate people can be said to not exist in real life thanks to how differently different people's bodies may respond to any particular method.

The "karate chop to the neck" version may have been removed from modern TV because if you hit the right spot it actually can knock you out, though not without serious risk of death. It utilizes the Carotid Sinus Reflex (the reason you should not take a pulse at the neck) and is very dangerous. There have also been depictions in productions as varied as the lighthearted I Spy and as dark as Callan in which neck-chopping unambiguously is shown to be fatal because it breaks the target's neck, which circles back to unrealistic — breaking a person's neck takes a lot of force.

Despite having very little grounding in reality, the Tap on the Head is still commonly applied in fiction — after all, Tropes Are Tools. Maybe The Hero is a bit too good at their job, or the Big Bad's minions are getting too big for their britches and need an attitude adjustment, or the Tagalong Kid needs to be stopped from suffering (or causing) a fatal case of Cerebus Syndrome. Sometimes a brief bus trip is just something the plot needs to proceed, and rendering the offending character unconscious is a quick and easy excuse to get the ball rolling without actually killing them off. It might be justified if the character who receives the blow has super or magic powers of some kind (such as healing factors or invulnerability), as that would allow them to shake off something that would otherwise cause a concussion.

Other methods to knock someone out quickly and non-lethally include:

• In Western media, there's the punch to the jaw (AKA a "knockout punch"). Again, in reality this could inflict serious injury to both parties. For the victim, this is indeed a reliable way of getting knocked out, as a precise punch to the jaw causes whiplash that can temporarily mess with the brainstem; because this punch knocks the victim out so reliably, they may sustain further serious injury without being able to protect themselves, such as from being continuously attacked by a particularly scummy opponent, or falling and striking their head on something, inflicting even more damage. As for the attacker, they could very easily break their fingers without hand protection; boxers and MMA fighters wear gloves to protect their own hands, not to protect their opponents' heads. The gloves offer only partial protection to the opponent's head^note The gloves may to an extent protect the other person's face from cuts and the like, but they cause more damage to the brain. When the striker's hands are cushioned by gloves, they can apply more force to the other person's head, causing the brain to be hit with more force.. Modern-day productions often depict the punch injuring the thrower's hand in some way, sometimes for humorous effect.
• Common in anime is the "sharp shot to the solar plexus", often used to subdue a struggling person. It makes it fairly easy to pick up the now-unconscious person and sling them over one's shoulder for easy carrying. Its effects in real life vary; the severity depends on several factors^note victim body build, tensed torso or abdomen, force of the blow, etc., a serious blow normally impacts the nerve bundle in the region and causes the diaphragm muscles to spasm uncontrollably, which makes any activity requiring air very difficult. It can cause unconsciousness in certain circumstances^note when the amount of stimuli (pain, shock) inflicted to the victim's nervous system exceeds the body's threshold to endure; typically when there is a large gap in body conditioning between victim and attacker (i.e an untrained or amateur victim being caught unaware by an expert martial artist), and is somewhat safer than a blow to the throat or the back of the head, but it is difficult to tell what amount of force will cause what damage. It is very easy to veer into excessive force and cause dangerous organ or nerve damage such as rupture and internal bleeding.
• Choke Holds, where an arm around the neck is used to cut off blood to the brain ("blood strangle/choke") or oxygen to the lungs (chokehold, stranglehold). Properly applied, this is a safer and more reliable way of causing someone to become unconscious (still used in judo/jiujitsu competitions to this day), but carries a risk of stroke or other dangerous problems if used on an older victim or one with a weakened circulatory system. It also tends to wear off quickly (as in, after a couple of seconds), or alternatively when it doesn't, cause varying levels of brain damage. Not depicted very often in film or TV as it's difficult to distinguish on screen between a choke hold and someone having their neck broken or being strangled to death, potentially giving the wrong impression if the intent is to show non-lethal takedowns.
• Another variant is instant knockout caused by shattering either a vase or lamp over someone's head or even just on their back. This is even more of a no-no in real life, as a fist made of flesh is relatively gentle compared to a hard object. Swinging a few pounds of porcelain at the noggin with enough force to shatter said porcelain is a change from "attempted knockout" to "attempted murder".
• Sometimes the knock-out victim will be hit with a Tranquilizer Dart instead of being hit. While this is a bit safer and more grounded in reality (as any park ranger can tell you), anesthesia is risky, as too small of a dose doesn't give the target anything worse than a moment of drowsiness, while an overdose could cause cardiac arrest. The exact height, weight, and species of the target must be known beforehand or else there's a risk of losing or killing the target or of your target waking up before you want them to and rampaging through San Diego or turning you into a chew toy. Of course, in fiction the dart will always inject the exact amount of tranquilizer no matter who it hits, and the victim will suffer no ill effects upon waking up. Further, it is often depicted as Instant Sedation, whereas real tranquilizer darts normally require a few minutes to take full effect.
• Another variant is Electricity Knocks You Out: knocking someone out via electric shock. A tased/shocked character will scream for a moment (maybe we'll see a brief outline of their skeleton) before they promptly black out. This is a bit more common in science fiction (where electricity weapons are more common), and is even less possible then most other versions in Real Life. In reality, tasers (briefly) incapacitate people via uncontrollable muscle contractions and pain, not unconsciousness, and on occasion, even this can fail; both barbs must hit the target and lodge for the circuit to complete, meaning that only one of the barbs hitting renders the device useless. Furthermore, some people can partially resist the effects of the taser due to adrenaline or the presence of some recreational drugs, causing the enraged target to begin blindly attempting to assault those trying to apprehend them. Tasers can cause dangerous medical conditions, even cardiac arrest, but if you lose consciousness due to them, you are unlikely to ever wake up. However, in fiction the tased person will, of course, wake up with no pain and suffering no ill effects.
• If played for laughs, the knock-out may be accompanied by Circling Birdies or a Cranial Eruption.
• Can induce moments of euphoria.

See also Frying Pan of Doom, Rolling Pin of Doom, Wrench Whack, Back Stab, Blinded by the Light, Choke Holds, Instant Sedation, Pressure Point, Put Their Heads Together, Flower-Pot Drop. Contrast Death by Falling Over. Often leads to Waking Up Elsewhere. Pistol-Whipping is a Sub-Trope. Non-Lethal K.O. is a related trope in video games. Can be used to initiate an Injury Bookend. A blow to the head actually causing real injury is a fairly common Surprisingly Realistic Outcome.

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