Biography
It's not always played for comedy, but seeing someone get struck in the crotch is usually just plain funny. Whether the object doing the striking is an errant piece of sports equipment or a deliberately placed foot, the end result is going to be a grown man doubled over and trembling with pain. Bonus points if he then hobbles away and says something in a high-pitched voice. Not only will everyone find this hilarious, but tape it and play it back for the guy and even he will probably laugh. At least, once the swelling goes down. Sometimes a cause of Amusing Injuries, especially if the victim is asking for it. In shows targeted at children, it's often a Dangerous Forbidden Technique, or at least treated as one in-story (see 3 Ninjas and Mighty Morphin Power Rangers: The Movie). In Japanese media, the blow is often accompanied by the sound of a bell.
Effectively, this is a human's version of Attack Its Weak Point for massive damage. A subversion of this is Balls of Steel, where a character — for whatever reason — does not take damage from a Groin Attack (or at least doesn't take extra damage).
This trope is made possible thanks to an interesting quirk in the human body’s design; as the testicles function best at a temperature slightly lower than the core body temperature, this is why they hang slightly lower, and can be raised or lowered by reflex activity to ensure they stay at the right temperature in relation to ambient conditions. Thus, compared to other body parts, even the other ones typically seen as weak points (stomach, solar plexus, toes, etc), one’s Crown Jewels are considerably less ‘armoured’, hence why striking them hurts so much.
This usually only applies to men. Female characters are rarely subjected to groin attacks of any kind, and when they are, they are also likely to just shrug off in a moment.note Female genitals also lack the squish factor that comes from swinging in the wind. On the symbolic level, a groin attack on a male — especially if it's delivered by a female — represents that male being brought low by a well-placed blow to the very source of his masculine pride.
In contrast to most groin attacks, groin attacks that draw blood or involve some form of mutilation are very likely not to be played for comedy — and owing to the Primal Fear of bad things happening to our nether regions, particularly nasty attacks of this nature can be downright disturbing. Apart from being a hallmark of the Lust variant of the Serial Killer, this form of attack is most often used as either a particularly vicious form of Cold-Blooded Torture or as a way for Antiheroes to punish rapists and other sexual criminals, though a particularly vicious Combat Pragmatist may also use this tactic as just one more way to even the score or gain the upper hand in a fight. It may still come off as funny, though, if the guy is perceived as having brought it upon himself, such as having his gun go off in his pants. See Crippling Castration for examples of groin attacks that lead to the unfortunate victim losing his organs/the ability to procreate.
Along with Taser Tag Weakness, the Groin Attack also seems to be very effective against Superheroes and Supervillains, although some of them are immune.
Compare Freudian Threat. For certain kinds of groin injuries (actual or threatened) specifically related to sexual encounters, see both Vagina Dentata and Man of Steel, Woman of Kleenex. Also see Standard Female Grab Area for a similar incapacitating spot. Eye Scream, Fingore, and The Tooth Hurts are other primal fear reactions. The Distaff Counterpart to this trope is Breast Attack, although women can be subject to Groin Attacks as well, despite what the Female Groin Invincibility trope would have you think. Often utilized by a Combat Pragmatist, and commonly followed up by Instant Soprano and/or Share the Male Pain. Not an uncommon aftereffect of Tar and Feathers. May be used as part of a "Balls" Gag, though the overlap is smaller than one might think. Near-Miss Groin Attack is when an aversion of this trope is Played for Laughs.
WARNING: No matter who you are, reading these may cause extreme paranoia about injury to the pubic area and wincing in sympathy pains. Also, this is never as funny in Real Life as it is on TV and can actually cause very nasty injuries, so unless you are in a real self-defense scenario, Don't Try This at Home.