Sam Vimes is familiar with giving and receiving, for one. Also from the Watch books, Carrot Ironfoundersson received a codpiece as a going-away gift from a friend of his (adopted) father, though he was initially naive enough to think no one would dare strike someone else there. He wore it anyway. A few days into the job, though, someone tried...and broke his knee on the "Protective".
One of these inspires a villain in Monstrous Regiment after he tries to put the moves on Polly "Oliver" Perks when she's dressed up as a boy dressed up as a girl. Yes, that makes sense. The same book also has a scene where the protagonist is bitten by a horse to the place where her family jewels would be, were she actually male (she keeps a bundle of socks there, instead). The sole male witness quickly faints, and after he comes to Polly hastily explains that her trousers were baggy enough the horse didn't do any damage.
Leading to a Funny Moment in which Polly, desperately trying to maintain the illusion and recalling what real boys do when they're subject to Groin Attack, laments "Ooh! Aargh! Right inna fruit!" and punches the horse on the nose.
One dwarven saying is, "When their hands are above your head, your teeth are level with their crotch." The implications water the eyes.
To Cohen the Barbarian and his Silver Horde, psychological warfare consists of spending the night before a big battle intimidating the enemy with chants of: "We're going to cut your tonkers off". Performing this operation on your worst enemy and then offering it as a present is likewise their idea of how to impress a woman.
Also from Guards! Guards!: Sergent Colon to Nobby Nobbs. "You know all about 'voonerables', Nobby. I've watched you fight." Unfortunately their attempted attack on the dragon's "voonerables" fails because it was a girl.
Mort gets one from Death himself. Even Cutwell had to wince.
In order to properly shoe unruly stallions, Jason Ogg threatens to do this to them. With a smithing hammer. Likewise, You Bastard the camel recognizes a similar implied threat in Pyramids, in the form of two bricks. This references an old joke about a bet between two French Foreign Legionaires, one of whom claimed he could make a camel jump straight up in the air...
Arnold Sideways of the Canting Crew, a band of near-legendary Ankh-Morpork beggars, is considered a useful asset in a fight despite having no legs because "a man with good teeth at groin height has things his own way". He also has a boot on the end of a stick, meaning that many thieves desperate enough to attack the beggars would find themselves kicked in the head by a man four feet high.
Granny Weatherwax gives an Elf a double handed punch in the area in Lords and Ladies.
In Unseen Academicals, after the Academicals win the Big Game, a furious Andy Shank tries to get one last cheap shot in by kicking Trev Likely in the fork... and nearly breaks his foot, because Trev is wearing a pair of micromail boxer shorts thoughtfully provided by armorer/fashion designer Pepe.
in Raising Steam Moist Von Lipwig aims a kick at the groin of a dwarf note who's sex is ambiguous like most Discworld dwarfs and prays desperately that it isn't female. The dwarf reacts in pain, and Moist takes that as confirmation that it's male.
Jim Butcher's Proven Guilty, in The Dresden Files, uses this near the end of the book, when Harry and the others are escaping from the bad guys, but are about to get overrun by trolls. Harry stops, turns, and uses his sword to stab the lead troll in the jimmies. This is accompanied by the line, "If you've got danglies and can lose them, that's the kind of sight that makes you reconsider the genitalia-related ramifications of your actions real damned quick."
In the short story "Heorot", Harry is up against a grendelkin, who's immune to Harry's magic. When the monster corners him, Harry gets some breathing room by winding up with his staff and getting him in the fire-extinguisher.
There's also the altercation with Caine a bit earlier in the story.
As he came in swinging, I snapped the lower end of my heavy staff into a rising quarter spin, right into his testicles. The thug’s eyes snapped wide-open, and his mouth locked into a silent scream. It’s the little things in life you treasure.
In another short story, "Day Off", Werewolf!Kirby is being chased by Mouse while chasing Harry's cat Mister due to the influence of psychic parasites. During the chase, Kirby knocks Harry down, and Harry gets trampled by a pursuing Mouse, who's paws happen to land "right were the damn dog always gets a man."
In the Red Dwarf novel Last Human, a character incapacitates a horrific rampaging leopard monster with a combination of 1. A serum that radically increases a person's luck and 2. A rubber band.
In an earlier novel, Infinity Welcomes Careful Drivers, a hologram attempts to thump a desk in frustration, only for his hand to pass clean through it and slam painfully into his groin.
In "Backwards" Lister earns a shard of glass through his crotch during a Virtual Reality gaming session.
Also in "Backwards" Peterson ends up in jail for stapling a shore patrolman's penis to his thigh. Upon being released, Peterson is warned that the patrolman is looking to return the favour with red-hot rivets.
When Kryten becomes a human being in "Last Human," one of his attempts to help the crew end with him tumbling down a flight of stairs, getting hit in the chest by an oxygen tank, and catching his groin on the tank's nozzle.
In the climax of "Last Human," Lister's Evil Twin shoots him in the groin with a rad-pistol, permanently sterilizing him. Or at least it would have been permanent if they didn't have the Luck Virus.
Lister's opening stint as a Hopper taxi-driver in Mimas begins with him accidentally biting a lit cigarette in half; naturally it lands in his crotch. After a few seconds of smoldering hair, Lister grabs a thermos and pours it over the flames, only to discover that it contained hot coffee; now in serious pain, his final resort is to grab another container for help. It contains upholstery cleaner. Ouch.
Colt's shot hit there purely by accident but that probably isn't much comfort to Johnny Nobody
This is one of Richard Sharpe's favorite attacks in his adventures, but isn't limited to him alone - a Portuguese soldier bayonets a French soldier in the groin in one of the books.
Probably the best example is when Sharpe is being tortured by a French Torture Technician who has 'always wanted an Englishman to experiment on' after Sharpe's beloved telescope (a present from The Duke of Wellington) has been smashed by the sadistic villain Ducos. Sharpe manages to grab the splintered end of the telescope barrel and stab the torturer in the crotch with it.
Yes, the fall of the Riders, the rise of the immortal tyrant Galbatorix, the near-genocide of the dragons, and the millions of lives lost to senseless war were a direct result of Vreal taking a kick to the nuts.
Uncle Toby from Tristram Shandy was bedridden for months due to receiving a large stone to the groin during the siege of Namur. Laurence Sterne intentionally plays up the Narm of the situation.
Simon R. Green's novels have plenty of non-funny incidents of this, often followed by killing the unfortunate bastard while he's down (Green's generally fond of BRUTAL fight scenes), but one of his Nightside novels had a comedy version involving a mousetrap.
Deuteronomy contains an instruction against groin strikes. To quote chapter 25, verses 11 and 12 (New International Version): "If two men are fighting and the wife of one of them comes to rescue her husband from his assailant, and she reaches out and seizes him by his private parts, you shall cut off her hand. Show her no pity." The implication is that going for the groin is fair game if you are e.g. in danger of Attempted Rape, but not if you aren't in immediate danger.
In To Kill a Mockingbird, Scout accidentally kicks a man in the groin when he is picking on Jem. The quote goes something like "I aimed for his knee but I kicked too high."
This occurs sometimes to private detective Spenser, in Robert B. Parker's series of novels. It is rarely effective because, as he points out to one female martial artist who tries it on him, it's a) not as painful as the media portrays and b) if you've been through enough other sorts of pain, you can work through it.
When Alanna was having bully troubles as a new page, one of her teachers suggested aiming below the belt. She did that the next time they were fighting, but while it hurt the bigger, older page, he still won conclusively - she had to learn a lot more dirty fighting tactics to give more than she got.
There's mention of Kel's medium-sized dog Jump leaping up and biting an attacker below the belt. And hanging for a moment.
Beka Cooper and the other Dogs in the Provost's Guard do this. A lot. Her books are noticeably coarser. They are protopolice, not nobles, and they're fighting for their lives a lot of the time, and in their time Tortall is a few rungs lower on the scale of cynicism and idealism than in Alanna's. A number of the people Beka comes up against wear codpieces - but a metal one that's not a solid scoop doesn't protect that well. In one fight, she grabs a "chunk of the inside of his thigh" and pinches with all four fingers and thumb while her scent hound bit his hand.
Also happens to Generator when she's trying to teach herself the basic kata for the nunchaku. With real nunchuks.
One of the villains in Doc Sidhe was known for punching his opponents in the groin. The main (not the title) character not only made and wore a codpiece, but studded it with shards of iron — and then left himself open for the punch.
In Shadows of the Empire, Leia eventually does this to her Smug Snake captor/wannabe seducer. The moment before it happens has been immortalized with this◊ Hildebrant Brothers card.
A parody gangster novel featured an assassin so twisted that he'd devised a hand-to-hand combat tactic where he reached down his opponent's shorts and tore off whatever he could grab there. He'd submitted it to a survivalist magazine's article series on dirty fighting, but was rejected.
This image from one of Ashida Kim's books. Thankfully, given that the guy's a known scammer it's likely he just made that up.
Joseph Wambaugh's The Choirboys includes an incident of a cop with an exaggerated sense of his own toughness trying to stop a fight by intimidating both combatants. It doesn't work out too well, resulting in what he describes later as "The Night My Balls Blew Up." He isn't able to get an erection for the next three weeks, and his wife tells a neighbor she's never had it so good.
In one of John Gardner's Bond novels, Bond attacks a fellow MI6 agent, a woman, who is the double agent he has been looking for, who betrayed and destroyed the spy ring she was part of. The fight begins with Bond kneeing her in the crotch. In the text, Gardner does point out that such an attack is painful for women as well as men.
In both of Aaron Allston's books in the New Jedi Order, it's seen that while Vong wear armored skirts, they apparently don't have any protection beneath them. Lando shoots one, and this is apparently more pain than even a Vong can endure, because it's easily dispatched by his terminator. Out on Coruscant, Mara encounters another. The viewpoint character glances away for a moment and looks back to find that the warrior...
[...] in the middle of a quite elegant snap-kick against Mara, was receiving her lightsaber thrust up and under his skirt plates.
The image of such an attack is invoked in Winds of Fate by Princess Elspeth. She follows a practice of her mentor Herald Captain Kerowyn: standing on the saddle of her horse, she drops straight down into her saddle. It always makes the boys wince or cringe. It seems, though, that the impact is too low for the testicles.
In Hell's Faire, Major LeBlanc punts the civilian technician helping run the damaged "Bun Bun" between the legs, for an earlier event caused by a wrong setting on a Geiger counter that resulted in the major stripping down for an anti-radiation wash-down, after being splashed by water that was thought to be highly radioactive.
In Yellow Eyes, one of the named Posleen tromping around in the Panamanian jungles has a Cayman bite on its genitalia, to which a Normal replies with its Boma blade, only missing due to the victim's thrashing around, and cutting off part of the God King's member instead.
Richard Marcinko enjoys writing these into his Rogue Warrior books. Stands to reason, since it's a highly efficient way of getting an advantage in a life or death fistfight. Despite these books being mostly Self-Insert Fic, with himself as The Captain, he is not afraid to describe himself on the receiving end of a crotch shot.
In one, he has to take a bunch of office-bound engineers and teach them how to play paintball. The dweebs learn quickly, and one deliberately aims for his crotch at point blank range.
In John Dies at the End, Dave gets into a fight with the character Shitload, who knocks him out with six successive hits to the groin. When Dave wakes up, the dog, Molly, walks over him, and all four of her paws land on his crotch.
In the bizarro storyMonster Cocks, this trope is both played straight and inverted. The hero, Jack, wishes to enhance his penis in order to win the heart of a co-worker, and orders a bunch of male enhancement treatments off the internet, at least three of which requires him to inject something under the skin of his genitals with some cousin of a piercing gun. The treatments prove to be successful—too successful, as his genitals become self-aware and attack and eat several people.
In The Kingdom Keepers this is how Philby's mother escapes from Luowski. "His mother bent her knee and drove the ball of her heel up and into a spot between the boy's legs that made Luowski's eyes squint shut as he screamed."
Played nightmarishly humorously in Dan Savage's book Skipping Towards Gammorrah, where he commits all Seven Deadly Sins in a grandiose manner. For Avarice, he goes on a nature retreat for rich people. It includes a very strenuous hike; he went commando because his underwear got soaked in sweat, but then his thighs started to rub together and chafe, then the rash started to bleed, then the sweat from his balls made it sting. So after a couple miles of misery, he shamelessly held onto his junk for the remainder of the hike. Sounds like the groin did the attacking in this case.
Among the unorthodox methods of the Analyst of Bagé (an overtly manly psychoanalyst created by Brazilian writer Luis Fernando Verissimo) is the joelhaço, a groin attack done with the knees (which the Analyst says he only does with men "because you only beat up women to discharge energy!").
Patient-I only know that I'm depressed, and this is the worst thing ever! Analyst-Worst than joelhaço?
In The League novel Born of Fire, Shahara kicks her future love interest in the crotch so hard that every time she attacks an enemy male in the same fashion (3 or 4 times during the book), he winces in sympathy, even though she was saving their lives.
Shay from Long Division whacks City in the balls with a stick for kicks.
In Robert B. Parker's Spenser novels, the title character is a skilled-enough fighter to usually block or dodge such attacks. One time a Groin Attack does land, he shows that he can willpower through it, much to the surprise of his highly trained female-martial-artist opponent. After he knocks her on her ass, he actually lectures her about not relying on the Groin Shot, as it's not as reliable an attack as she thinks it is.
In the Dean Koontz novel Life Expectancy, protagonist Jimmy uses a nail file to the groin to disable Punchinello long enough to get himself and Lorrie clear of both their armed captor and the bombs he's placed. (This event also figures to an extent in later plot.)
In the Inheritance Cycle, said to have been used in a duel by Galbatorix taking place a long time before the events of the book. The act was deemed "dishonorable," or something to that effect. Doesn't help that the story describes it with double-take language: the guy gets struck "in the fork of his legs".
Stephen King apparently has some fascination with this trope.
Gerald's Game opens with the title character suffering a fatal heart attack after his wife Jessie puts a knee where it counts to stop him from raping her.
In The Dark Half, villain George Stark combines an old fashioned straight razor, an upward slashing attack, and the groin of an unfortunate cop. All described with typical King skill. Did you just wince? Imagine reading it.
In Dreamcatcher, one character meets his death at the teeth of one of the weasels, which first attacks the soon-to-be-deceased's groin. (in the film version this happens to a different character)
"The Body", later made into the film Stand by Me, is discussed here (2 separate mentions of groin attacks).
In Needful Things, a police officer trying to break up a riot is shot in the groin.
In "Chattery Teeth" (a short story in Nightmares and Dreamscapes) the eponymous wind-up novelty toy ends up biting a carjacker to death. Guess whether it goes for the balls.
Henry Bowers, the human villain in IT, takes numerous hits to the groin. The last time it happens he even starts to bleed. Also in It, Beverly hits her abusive husband on the groin with a belt.
In The Stand a prison guard pays an inmate to knee Lloyd in the groin, after Lloyd insults him.
In Wolves of the Calla, when the Hitler Brothers ambush Callahan in New York, one of them grabs and tightly squeezes his scrotum to incapacitate him with pain.
In Rose Madder, Norman tortures information out of a man who saw Rosie run away by repeatedly squeezing his scrotum until he passes out from the pain.
In one of The Dark Elf Trilogy books, Drizzt kicks a mind flayer between the legs without knowing for sure if it had anything significant there to be kicked in (mind flayers are hermaphrodites).
Unsurprisingly enough, there are few indicators by the D&D rulebooks for one side or the other. Mind flayers reproduce asexually, but since they derive their bodies from humanoids that get their larvae inserted, their bits may or may not vanish during the transformation.
In Wizards Three (Dragon # 219) Shaaan tried this on Elminster... He knew in advance with whom he had to deal. "Oh, did I forget to mention my new steel codpiece?"
In Piers Anthony's Tarot series, the protagonist is forced to choose between surrendering his eyes or his testes to proceed further on his quest. Because he's a monk sworn to celibacy and his quest is extremely important, he chooses the latter. Subverted in that the amputation is performed painlessly by magic.
The extended description of the heroine "lodging her sandaled foot squarely between the shaman's testicles" in The Eye of Argon. Especially because the description of the reaction to the Groin Attack takes several (extremely Purple Prosed) sentencesto describe.
In 1632, Rebecca Stearns fires a sawed-off shotgun into a Croatian soldier's testicles. At point blank range.
The female warrior protagonist of Iron Dawn devised an underhanded ax blow — with a two-handed stone axe — with which she took a pelvis-splintering revenge upon the bandits who'd gangraped her. When an enemy she kills with this move is reanimated as a zombie, his entire lower torso has to be held together with leather straps.
A flashback scene in Headhunter involves the future serial killer watching an S&M aficionado chop up a prostitute. The naked ax-wielder had a dozen needles shoved through his penis at the time.
Parental threats to the genitals are common in the backstories of fictional serial killers. In Red Dragon, Francis Dolorhyde's abusive grandmother punished him for wetting the bed by placing the blades of a pair of scissors around his penis and threatening to cut it off.
Rainbow Six has Ding Chavez threaten to cut off a terrorist's vitals, though he ultimately doesn't do it.
The Shattered World:
Inverted by the leader of the Cthons (a demonic subterranean race), who has a live snake for a penis. It bites.
Played straight in the same novel when King Troas attempts to have his way with Ardatha Demonhand. She's not having any of it, and retaliates with a scalding-hot application of her namesake, directly to his scrotum.
Jack Fleming from The Vampire Files can usually wipe the floor with gangsters in a brawl, but being held down by a bunch of them while another moves to stomp on his privates is terrifying enough to force even him into Super Smoke form.
A villain in the NUMA Series novel Inca Gold has the female lead hostage and details the sexual tortures he's planning to subject her to. At that point, Dirk Pitt sneaks up, jams a gun into the guy's pants, and pulls the trigger.
Black Hawk Down: In the novel written by Mark Bowden, when the Somalis capture Mike Durant after his Black Hawk helicopter is taken down, one of the Somali women goes towards him as he is being carried away and "yanks" at his penis and testicles.
The King of the Crags by Stephen Deas has a... memorable example. With a crossbow.
In A Song of Ice and Fire it's strongly implied that Ramsay cut off Theon's penis, probably after skinning it.
In Death: This trope has popped up a few times. Eve Dallas takes down the murderer in Visions in Death hard this way.
There's a book, can't remember its name or even what it was about, whose cover shows a woman's stiletto heel coming down on a walnut. The imagery is...striking to say the least.
In An Uncertain Place, by Fred Vargas, Emile le Bastonneur manages to get away when the police want to arrest him for Vaudel's murder after hitting Mordent in the groin and Violette Retancourt in the ribs. Most of the Brigade being male, the state of Mordent's testicles is a subject of concern among them for quite some time... although this is inverted in the TV movie, where Commissaire Adamsberg checks on Retancourt multiple times, whereas Mordent's family jewels are never mentioned again.
In When the Devil Dances, Captain Elgars disables an attacker with a kick to the crotch when ambushed in a Sub-Urb passageway. In a subversion, the female victim definitely does feel it, reacting as a male would when the trope is being played straight.
Under a Graveyard Sky: In a discussion on how to deal with infected Technically Living Zombie security people aboard a cruise liner who are wearing body armor, Faith suggests a chainsaw. When Fontana points out the kevlar armor would jam the chain, she says "come up", and makes a motion of cutting up between the legs.