In First & Only, Jantine Patricians attack some Ghosts with this, including Kick Them While They Are Down; they kill three and render a fourth Ghost critical, and a fifth Ghost escapes only because they take him alive.
In Ghostmaker, when Gilbear walks the picket and disapproves of how he finds two Ghosts, he inflicts a No-Holds-Barred Beatdown, including Kick Them While They Are Down. Fortunately, Corbec interrupts.
In The Armour of Contempt, a gambling den sets out to beat Merrt to death in one of these.
About halfway through The Pendragon Adventure, in The Rivers of Zadaa, Saint Dane amuses himself by taking the form of a Giant Mook among the local military and effortlessly knocking Bobby around. This isn't it. Bobby, strapped for any physical response, gets under Saint Dane's skin with an impromptu Breaking Speech about how this is only a diversion from all the times he has failed, and how, in the end, he is destined to lose. In response to this, Saint Dane loses his cool the first time in the series, goes completely berserk, and beats Bobby within an inch of his life. Just to drive home how bad it is, Bobby spends a great portion of the book recovering from said Beatdown. His doctor and Loor specifically point out that normally it would take months for him to recover, and he'd never get full functionality from his body again, but beats the odds and somehow recovers fully. At first the only thing he could move without extreme pain was his toes.
In Graham McNeill's Warhammer 40,000Ultramarines novel The Killing Ground, in their third ordeal, Leodegarius defeats Uriel and Pasanius, knocking Pasanius unconscious and leaving Uriel unable to rise. Uriel, angry that this man, who should have fought beside them, is going to kill them, tells him to Get It Over With. Whereupon Leodegarius tells him that the ordeal is to lose, because the only way they could have defeated him was the use of warp-based powers. Failure has shown that they don't have them — and they are promptly hauled away from medical treatment that restores them to fitness within hours.
In Turn Coat, book 11, Wizard Listens-To-Wind delivers one of these to a Skinwalker, which is a nigh immortal, semidivine shapeshifter that feeds on magic. He does so in a Shapeshifting duel, eventually making the Skinwalker turn into a minor Eldritch Abomination and fly away screaming.
The only person we know of who was able to kill one was Morgan, who did so by leading it on a chase that ended in Nevada, where he went into the Nevernever and stranded the Skinwalker there. The Skinwalker was then hit by a nuclear bomb test.
Harry Dresden himself is not a stranger to being on the receiving end of these. During Grave Peril, where he experiences that being captured by Red Court Vampires isn't fun.
Harry tends to inspire this kind of feeling in most of his enemies, even as it's mutual. In Dead Beat, Cassius repays a No-Holds-Barred Beatdown Harry gave him with brutal murderous intent. It could easily be the Darkest Hour of the book, since Cassius explicitly said he would kill him slowly and very painfully. He gets pretty far, too.
Ender's Game has the eponymous hero deliver two of these, both to boys bigger and stronger than he. Ender doesn't pick either fight, but neither of his opponents is prepared for Ender's thorough Combat Pragmatism, and he really, really doesn't like bullies. They both end up dead.
In the original, it may not happen to a hero, but it's jarring enough. So far, we've only seen normal battles in a siege, and most of the plans have been sort of comic-book level: climbing over the walls via a tree, tunneling under, etc. Then Cluny finds out he's been betrayed by the fox "healer" he keeps around, and simply has his henchmen beat her and her son, stab them to death and dump the corpses in a ditch. Her son survives, unfortunately.
In Mossflower Martin the Warrior (a mouse) is on the receiving end of one from Tsarmina (a European wildcat), who repeatedly beats him into the ground, while taking comparatively minimal damage herself. Only Martin's determination enables him to "win" the fight, when Tsarmina, convinced that he is somehow incapable of dying, panics and flees.
Another one happens to a vermin Mook in Rakkety Tam, who is sent to scout out Redwall. He runs into a Long Patrol hare that's famous at boxing, and confidently thinks he can kill the "big rabbit". The hare in question beats the ever-loving snot out of him, partly as revenge for ten other hares that were killed and eaten by the mook's boss, and second for calling him a rabbit. This also happens to heroes, from time to time.
Gabriel's brutal beatdown of the captured Lymond in Pawn in Frankincense, the fourth novel in Dorothy Dunnett's Lymond Chronicles.
A common theme in the Star Wars Expanded UniverseX-Wing Series. Since it's kinda a war, shooting an enemy in the back while pretending to be one of their allies is a lot more acceptable than in other settings, but things like enhanced Ewoks wanting to slaughter unarmed scientists for torturing them is frowned upon. The Starfighters of Adumar book takes this to its logical conclusion; Turr Phennir's compliance with highly formalized and regulated but fatal beatdowns is monstrous, while Janson's beatdown of a man he disarmed to save a woman's life is a glorious Crowning Moment of Awesome.
1635: The Canon Law features the character of Quevedo. He is massive pain in the ass who orchestrates a number of plots to sack Rome and murder the pope. He eventually confronts Ruy Sanchez, the man who trained him long ago and is currently trying to save the pope. Ruy merely takes advantage of a flaw in Quevado's fighting style that he (Ruy) never bothered to fix and stabs him in the throat.
Hypatía Belicia Cabral, the mother of Oscar, is viciously beaten in her younger years for having an affair with the husband of Trujillo's sister. After working her over with fists, the dictator's thugs used nightsticks.
Thirty years later, Oscar gets an equally brutal beating from two other police thugs for trying to pursue a relationship with a prostitute that a captain was in love with. He also survives, barely.
Heathcliff does this to Hindley midway through Wuthering Heights, shortly after Catherine's death. Of course, earlier in their lives Hindley had plenty of times the opportunity to do this to Heathcliff, at least once using a whip.
Liesel delivers one to Ludwig in The Book Thief. He pushes her too far and she takes out all of her anger and grief out on him, winning the fight before Ludwig even knew he was in a fight. The only thing that stopped her was seeing a boy who was enjoying watching Ludwig get beaten up and Liesel reached up, dragged him down, and beat him up as well.
During The Will Of The Empress, Berenene decides that she wants Sandry- and her wealth- to stay in Namorn, and Sandry's foster-siblings (who are all powerful mages) to stay as well and serve her. After Sandry is abducted by a guy who wanted to marry her without her consent, all of the siblings tell Berenene to fuck off, at which point Berenene decides that they're only being so bold because they have Tris, who is one of, if not the most powerful mages on the planet, and who has incredibly rare ambient weather magic. Berenene's solution is to ask her curse-wielding second-in-command to make one for Tris. It knocks her down a flight of stairs, sending her bouncing and cartwheeling instead of sliding or tumbling, and breaks or fractures nearly every bone in her body, but doesn't kill or permanently disable her. And it only makes the four even more pissed off.
Those That Wake has a heroic version in its sequel, What We Become. Rose viciously beats Castillo with a chair, saving herself, Arielle, and Aaron.
Any ship that goes up against MV Oregon gets on the receiving end of one of these. What looks like a rusted tramp freighter on her last legs is actually one of the most advanced warships in the world, armed with enough weapons to put down a small army. She once exchanged broadsides with a fully-armed Libyan destroyer, and suffered only cosmetic damage and some minor injuries to her crew while the destroyer saw its main batteries destroyed within minutes, its bridge mangled, and a good portion of its personnel reduced to red smears on the deck. The only reason she didn't sink the destroyer was because doing so would have caused an international incident.
In the start of The War Gods series, Bahzell walks in on Harnak beating and raping a palace servant. Since his kind particularly believe that Rape Is a Special Kind of Evil, Bahzell leaves him with two open fractures in his ribs, nine teeth gone and four more broken enough to need pulling out, one eye swollen shut, broken nose and a lump the size of an egg in his forehead.
The Hunger Games: Given the nature of the beast, it's an inevitability. Even outside the arena, Cinna receives a nasty one as Katniss watches helplessly. And they never saw him again.
Poor Han Solo in The Black Fleet Crisis. He is captured by the Yevetha. They try to force the Republic's hand by beating him nearly to death and then sending Leia a video of it.