[James Potter] accidentally kicked Lucius in the balls eight times as he stood up with the man's wand.
In Empire when Snape is teaching Harry etiquette of the wizarding world it's related that the appropriate way of meeting and greeting harpies is to leap around on one leg so that they'll laugh and forget to castrate the male wizard greeting them.
In the Pony POV Series, Shining Armor receives a pretty brutal one from General-Admiral Makarov (the Big Bad of his arc) during their fight. It involved Makarov's antlers and had enough force to throw him into the air. Fortunately, Shining had armor protecting him, but still took a hard enough hit to disable him for a time and leave bruising. While played for drama at the time (since Makarov IS trying to kill him), the bruising is played for laughs later on, when Minuette is helping a doctor patch him up and seems a little TOO interested in checking the damage.
In Six Brides for Two Sisters, Shining Armor mentions how Cadance has the strength of an earth pony and "shouldn't kick a pony there unless you're absolutely sure," heavily implying this.
Shining Armor can't catch a break and in Stallionsof Harmony Verse gets one from Rainbow Dash, after tackling her into bushes in attempt to hide her from Blueblood. The way it looked, she was fully justified in treating him like a molester.
In Kitsune no Ken: Fist of the Fox, Suigetsu makes an attempt to hit Naruto in the head with a baseball during their physical education period at school. Naruto's response? He hits Suigetsu's very next pitch back at Suigetsu and straight into his nuts. Cue Share the Male Pain from every guy in the vicinity.
Suigetsu:(in pain) I can't feel my mini-me...
In Naruto Veangance Revelaitons, a few cases happen.
When Ronan gets captured by Madara and fed Indian food, he retaliates by punching Madara in the groin, but avoids touching his penis because he doesn't want to be seen as a homosexual.
Shortly after Ronan frees himself, he finds Taliana, and shoots her in the vagina, resulting in her getting s "chunky organism".
In Sailor Moon Princess, after a wild party, the girls search through Mamoru's laptop only to find erotic picture of them on there, so when he enters the room, both Rei and Makoto kick Mamoru's groin in anger.
However, they later find out that it was really Haruka's laptop.....
Guide Me Home; during a sparring match, Hakoda pins Ursa against a wall and accidentally touches her burn scar. Ursa panics, Groin Attack ensues and Ursa is completely mortified afterwards. Yes, that is an actual tear jerker example of this trope.
Lois Busts Superman, not only she busts Superman's groin multiple times after weaken him with Kryptonite disguised in her heels, but she also raped him. And in the sequel, she did this to Hulk and even get pregnant of their child.
The Seed of Batman, where Batman suffers multiple doses of Groin Attack, blowjob, handjob, etc. For huge doses of humiliation, those who give him this are prostitutes, whose boyfriends (or pimps) have been imprisoned by Batman so they want to take Revenge by humiliating him. In Chapter 3, Candace and a henchwoman take it further by raping him while framing him as if it was Batman who raped them.
In "Ah,Nuts!", John and Roy tangle with a druggie who turns violent and directs his anger at John, biting him in the groin. He yelled that he hoped he bit it off, but John escaped with a wound on his thigh and scrotum that Dr. Brackett had to suture at Rampart. He is embarrassed, but Roy reassures him that he really had nothing to be ashamed of, and that the guy was awful for wanting to permanently disfigure him.
In The Birthday Present, Bellatrix Lestrange tortures Snape with a Cruciatus curse to the groin area, which leaves him impotent.
In Cub Ron tried to pull ex-girlfriend Hermione into an alcove and when he turned around to talk to Draco Malfoy she kicked Ron in the balls.
In the opening scene of Mirrored, Voldemort demands that Harry kneel before him or he will kill Ron and Hermione. Harry complies but takes this opportunity to punch him in the balls. Ron decides that was the most awesome thing ever (and won't shut up about it) while Hermione cautions that this will no doubt have repercussions seeing as Voldemort was only out to kill him before.
Harry: Hello, Krum. While I know that I'm probably going out of bounds with this, but I just wanted to let you know that Hermione is my best mate—she's like a sister to me. So if you hurt her in any way, I'll not only hex your balls off, but I'll also make the rest of your life a living hell. Just so you know—for future reference.
In Souls Abound Millicent Bulstrode kicked her father in the crotch when he tried persuading her to let Voldemort's spirit possess her body.
In Unconventional Harry Ginny hit Draco Malfoy in the crotch with the bag containing Harry's Triwizard Tournament winnings.
This is lampshaded by Deimos's statement: "The final tenet is fight dirty. This isn't a duel nor is it a time to be fair. Gouge your opponent's eyes, gang up on one opponent, use groin attacks, whatever it takes it defeat your opponent."
One chapter has an enemy dinosaur bound to a tree and beaten severely, including several kicks to the groin.
Another chapter has Ducky's mother, armed with twin sticks disable another dinosaur by striking his weapon arm with one stick, tripping him, then kicking him in crotch.
The most brutal groin attack in this story involved a dinosaur kneeing his enemy in the groin, ripping out one of his opponent's eyes, tripping his opponent and almost literally ripping his opponent's head off.
They're reptiles. How does that even work?
Research be damned! It's too much of a good story to let facts get in the way.
In The Legend of Spyro: A New Dawn, Cyros kicks her younger brother Pyros in the groin, then stomps on him there when he says she'll lose a bet, one of her Berserk Buttons. She does it again in the final battle between them to gain the upper hand in their fight.
In The Life And Times Of A Winning Pony, this is taken more seriously than most examples when Cloud Kicker delivered a nasty blow to Rainbow Dash's groin, resulting in her nearly bleeding to death. The incident was probably also a major factor in Rainbow Dash's asexuality
In the Empath: The Luckiest Smurf novel, Smurfette gives one to Hefty for his saying that Empath couldn't possibly feel a thing for her, with her retort being that Empath would feel more for her in his heart than he would in his private area (insinuating that is how Hefty feels for Smurfette).
In Chapter 12 of An Unexpected Child, Bruce actually punches Alice in the dick, causing her to fall over and knock down a pillar, which then falls on part of the circus audience and crushes them to death.