Used repeatedly in the blog novelFartago. Punching in the crotch seems to be Farta's preferred method of exacting retribution on Tago for any pain Tago causes Farta. Later justified as the pre-monolith tribe's method of exerting alpha male authority and punishing losing contenders, and also subverted in that the scene when the entire tribe lines up to punch a losing alpha male in the crotch is definitely notplayed for laughs. The cries of anguish of the abused loser depress Farta and Tago so much, they're unable to do anything but drink.
Aaaand...there was the first Nerd vs Critic battle, when they fought with light sabers, but the Critic accidentally had his upside-down...
And during his series, video game confessions, where he's a bartender at a restaurant that sees many video game characters, Samus is apparently the giver of 2 crotch shots, and I mean "with the lazer gun" shot, to both Justin Bailey, and Leisure Suit Larry, because she hates it when people ogle her.
In Kickassia, the Critic finally got to do this to someone else, showing Lee one of the few downsides of being three-dimensional.
In Nostalgia Critic's review of Casper, an animated Casper infuriated by the Critic's panning of his film states that if he can't have a lasting impact on popular culture, he can still have one on his balls. Cue Groin Attack.
In the "You're A Dirty Rotten Bastard" Christmas Special, before meeting his guardian angel, the Critic clamps the poor guy's balls.
Happened a few times in Suburban Knights, especially with Malachite using magic to force Nostalgia Critic to hit himself in the balls, 15 times.
After viewing Zardoz, Oancitizen takes the "Gun is Good, Penis is Evil" message too literally and goes to the bathroom to shoot off his groin. He somehow misses.
At the end of the Nostalgia Critic's review of Man of Steel, Superman opts to defeat Zod by Heat Vision castration instead of killing him.
In the NC's review of Nicolas Cage's The Wicker Man, in order to get Critic to reference the infamous NOT THE BEES scene, Tamara holds onto him while Malcolm hits his groin with a baseball bat. Every time the Critic is hit, his voice gets higher.
The Angry Joe Show: At the end of his review of the Deadpool game, Joe is confronted by Deadpool, angry at dissing his game. Joe manages to convince him the game was lacking... in kicking guys in the balls. Deadpool agrees, and thanks Joe... with a punch to the nuts. After that, Joe swears to not review any Deadpool game again.
And later on, when stranded with Splinter, Shredder runs off, going, "Man, fuck this shit, you're gonna kick me in the nuts! I'm off this motherfucker! Sheeeeit...fuck you!"
A party themed Happy Tree Friends Smoochie involves the character Nutty getting hit in the groin with a yo-yo. To make things worse, it continues to spin rapidly, with the frition causing smoke, resulting in him bursting into flames, with all the while Nutty screaming in agony. It's the first item on the list, the toy.
A series of videos on YouTube entitled "Kicked in the Nuts" involves a man in an orange afro wig kicking (supposedly) unsuspecting people in the nuts. They invariably react at first with pain and/or anger, until he points at the camera and informs them that "You've been kicked in the nuts!", at which point they're just happy to be on camera.
This episode of Rooster Teeth's Red vs. Blue does this to hilarious effect. It defies description, but not count: 7 separate groin attacks.
In the Super Mario Land series of web videos on Newgrounds, specifically the ending clip of the first episode before the credits, Mario attempts to go down a pipe, only for a fist to emerge from the pipe right underneath him, with Mario expressing a shocked face as the camera pans up to the sky to which a loud holler is bellowed.
Green Goblin: "Yeah. The Joker tends to go for the really obvious jokes, doesn't he?"
As part of a montage of Captain Hammer's jerkass humiliations against a helpless Dr. Horrible, he gives the doctor both a knee to the groin and an extremely painful-looking wedgie.
Lady Lumps VS Boy Bumps has hundreds of examples with characters from all kinds of different series. You can even fill out a template and ask the creator for your own character to be in an animation!
This happens to Mr. Mack in Episode 51 of The Most Popular Girls in School, after he asks Brittnay Matthews to try to simulate a resolve with Jenna Darabond. He tries playing Jenna, the one who seemingly blew up Brittnay's car, in a recreation of the scene, and well...he asks Brittnay if those were cleats on her shoes.
In "Yellow", Yang interrogates Junior by grabbing his crotch and squeezing. His voice goes high-pitched and girly sounding until she lets go.
In "Breach", Coco boots a Beowolf in the crotch. It staggers and whimpers, right before she crushes its skull with her handbag.
"New Challenges" sees two flaming coconut propelled through the air toward Scarlet during a tournament march. He gets smacked by the first one in the face, leaving him staggered enough to not expect the second one that hits lower from off-screen, knocking him out from the tournament.
In The Salvation War, Uriel gets this with two AIR-120 missiles it's the least of his worries.
Not surprisingly, the Whateley Universe stories have many, many instances of this, both done for laughs and in earnest (see below):
'The Second Book of Jobe' has a disturbing number of (generally well-deserved) groin attacks, most of which straddle the line between drama and lulz, such as when a now female Jobe's recently created bio-prosthetic penile replacement is forcibly removed by a panicked Misty.
Phase gets poorly repaid for his generosity when Fey and Generator play a prank on him by switching on the 'special' features of one of the showers (which he'd paid to have installed as a gift to his female cottage-mates) while he is washing up.
In another case which could be read either seriously or for fun, the battle at the restaurant in 'Ayla and the Birthday Brawl' is literally kicked off by Phobos when she retaliates against a mercenary who tried to hold her hostage. Phobos is another Exemplar, and she has goat-like legs and hooves, which leads to the merc getting a world of hurt. Every male (or former male) in the room is stunned for several seconds before the fighting resumes.
Generator builds a set of nunchaku, with the predictable result while practicing with them.
The second installation of Awkward. contains two in quick succession. First Alex against Lester in a staged fight to make Kevin look like a hero (which later leads to some unforgettable mental imagery when Lester remarks, "It's like a cat tried to suck my dick."), then Henry against Kevin. He takes a run at it.
In Worm, Taylor needs to incapacitate Lung as quickly as possible, so she uses her bug control powers to make black widows bite his genitals. Fortunately for Lung, Good Thing You Can Heal is in full effect, at least, once the rotting is finished.
As has already been said, Whateley Universe has several serious takes on this as well.
Not only does Counterpoint deliver an Exemplar-strength kick to Jobe's nads (which speeds up his Gender Bender transformation), but more seriously, Carmilla later detaches his penis outright while completing the change.
In what is probably the most tragic and disturbing case, Generator, after returning to being male after managing to become female temporarily, takes a scalpel to her male genitals and cuts them off, repeatedly, while the keep regenerating, finally passing out from blood loss after over an hour of frenetically hacking at herself.
After Carl de-pantses Paige (whom he didn't believe was a Hermaphrodite) at a family gathering, she proceeds to open up a can of whoop-ass on him that even the other weres in the room were stunned by, including a series of vicious blows to the gonads. She had to be restrained from cutting them off once he was down, and while it was clear everyone thought he deserved it (and knew he would regenerate soon enough), the sheer intensity of her assault was considered excessive.