The last duel between a captured Worf and the Jem'Hadar First running the prison camp. Worf's refusal to quit even in the face of such a relentless example of this trope garners him rather a lot of respect in the First's eyes: "I cannot defeat this Klingon. I can only kill him, and that no longer holds my interest."
This happens after Worf (and Martok, though we never see him fight the Jem'Hadar on screen) are badly injured and exhausted after days of fighting the Jem'Hardar as part of a Dominion training exercise. Most of the previous fights—at least the ones we see—end with Worf killing his Jem'Hadar opponent with his bare hands. Dialogue states that Worf bested at least seven opponents before he had to face the Jem'Hadar First.
Colonel Kira has handed out a few no holds barred beatdowns over the course of the series. One notable example includes Way of the Warrior Part 2, in which Klingons have boarded the station. One of the Klingons who beamed into ops stabbed Kira in the kidney. Kira pulls the dagger out of her back and then beats the crap out of the guy who put it there.
Sisko gives them out often enough that SF Debris theorizes that he solves all his problems by punching them.
An example that led many people to guess he was the Big Bad for season 1 of Veronica Mars was when Aaron Echolls beat the hell out of his daughter's abusive boyfriend. To the soundtrack's strains of "That's Amore." It was awesome, and yet hard to watch.
24: Jack Bauer. Every time a villain gets his hands on Jack, you know it's not gonna be pretty.
A particularly brutal example is in Season 6, when Jack and Abu-Fayed finally face off. It starts with them savagely beating each other, then Jack breaks Fayed's arm with a wrench, and Fayed responds by beating Jack with a pipe. Fayed then starts beating Jack's injured ribs, only Jack to wrap a chain around his neck and kick him in the groin. He then whispers "Say hello to your brother" to Fayed, before he activates the chain hanging him. It's easily the most brutal fight of the series.
The episode "Objects in Space" is one long, drawn-out version of this, where Jubal Early proceeds to systematically beat up everyone on the ship who even tries to stop him (or looks like they might possibly try to stop him at some indeterminate time in the future). Fortunately, River and Mal manage to outsmart him.
Also happens in "Jaynestown," to Simon at the hands of Jayne's old partner.
The final fight (if you can call it that) between Jayne and said partner is also pretty one-sided and wince-inducing.
In "Shindig", there is a swordfight variant of this as Mal takes on Atherton Wing, and proceeds to nearly be cut to ribbons by his superior swordplay. He comes out the other end in pretty bad shape.
Season 4, Keamy, tracks Ben down to The Orchid's underground level and starts searching for him, uttering a villainous monologue as he does so, but then he makes a mistake by talking about how he, just a few episodes ago, murdered Ben's daughter in cold blood right in front of him. Ben, who is hiding away, hears every single word of what Keamy says, and, after Keamy converses with Locke, he gets his payback- Ben leaps out of a locker, viciously beats Keamy to the floor with a nightstick, and stabs Keamy twice in the throat with his own knife, all the while yelling in a feral rage, "You killed my daughter!" Keamy got what was coming to him.
Ben is typically the victim of these no holds barred beatdowns. Particularly vicious ones were by Sayid in Season 2, Jack in Season 3's finale, almost had one from Sawyer in S4 and an especially brutal and bloody one in S5 from Desmond no less. Who previously never lashed out in such a violent manner, but there ya go. Never mess with the Scotsman. Even nice guy History teacher alternate universe Ben got one, once again from Desmond. Though in a school parking lot this time.
Sawyer got his fair share from Pickett in Season 3. And Locke beat 7 shades of shit out of Mikhail in one of his many Crowning Moments of Awesome.
And then there's Jack and Sawyer beating the absolute living crap out of each other in the Season 5 finale.
And then there's the Smoke Monster's Temple rampage in season six.
They sometimes have one of these near the beginning of the series when the Big Bad or The Dragon deigns to pound the Rangers flat in person, before ultimately deciding that they are Not Worth Killing. This editor remembers Rio from Gekiranger and Wolzard from Magiranger pulling at least one of these each.
The Monster of the Week will occasionally end up on the receiving end of one of these. Or, in the case of Cyclopsis, on the giving end.
Mighty Morphin' Season 1, where Goldar, Scorpina, and the Green Ranger work together to take down the Megazord. Some monsters such as Cyclopsis, Samurai Fan Man, the Frankenstein Monster, and Mutitis would also hand these out to their zords, including the stronger formations. For example, the Dragonzord in Battle Mode could do little more than make the Samurai Fan Man lose his balance, the finisher was actually used not to win, but to free a trapped Kimberly so they could form the Ultrazord.
In VR Troopers, Grimlord's second in command Decimator would usually mop the floor with Ryan Steele in combat, but when Decimator seemingly mortally wounded Ryan's father, he found himself on the receiving end of one of these delivered by Ryan. A shocked Decimator fled after a brief "battle" on his go-kart.
In one particularly memorable sequence, Londo Mollari arranges for Lord Refa to meet his end this way at the hands of angry Narns. Ironically, his primary motivation was revenge against something that someone else had done, but don't worry, all the other crimes checked out. The guy had done more than enough to earn his fate.
An element of comedy is added to this scene by the fact that the death is accompanied by a gospel song about Judgement Day called "And The Rock Cried Out, No Hiding Place". No hiding place, indeed.
Marcus's fight with Neroon in "Gray 17 is Missing" also comes close to this trope, though Marcus does get a few good hits in before being pounded into the deck. He only survives after calling on the name of Valen, the Minbari's most holy figure, at which point Neroon realizes that he has been acting dishonorably and retreats.
Sheridan gets one of these in "The Face of the Enemy" after he is tricked into exposing himself so he can be captured by those loyal to the Clark regime. The sequence, one of the most elaborately shot in the series, is powerful and disturbing in the way it contrasts Sheridan's messianic, larger than life image with the objective hopelessness of his situation, using multiple Hope Spots and Sheridan's refusal to give in. It's also a culminating moment in the breakdown of his relationship with Michael Garibaldi, his old friend who was made to betray him, making for an exceptionally powerful scene. The Passion of the Christ goes to the same well — not surprising considering the biblical references that lead up to the scene.
In Rescue Me, Tommy delivers one of these (with several people trying to hold him back) to his brother Johnny when he discovers the latter has been sleeping with his wife. At one point he puts his head through a car window.
In the 100th episode of Criminal Minds, Aaron Hotchner goes toe-to-toe with The Reaper. We've already seen the Reaper clean Hotch's clock in "Nameless, Faceless", but it's different this time: Foyet has just killed Hotch's wife, Haley, and made it clear that if Hotch doesn't stop him, he'll kill Hotch's six-year-old son Jack next. Hotch empties his clip into Foyet, then, when it's revealed that Foyet was wearing full-body armor, throws him through a table and beats him to death with his bare hands. It takes Morgan to finally pull Hotch off. A hell of a way to invoke Not So Stoic.
Previously, an unsub whose daughter had been killed while he was in prison kidnaps father/daughter pairs, then forces the fathers to beat other kidnapped men to death or watch their daughters be murdered. Ordered to finish off an already-stunned opponent, one father has no choice but to keep slugging his helpless foe, pleading "I'm sorry" with every blow.
In The Wire, Michael asks Chris Partlow to kill his stepfather, Devar. Normally Chris carries out hits in a dispassionate manner, killing with a headshot. However, it's implied that Devar has sexually abused Michael, and upon hearing Devar admit to raping other inmates in prison (or at least, that's what Chris takes from it), Chris beats him to a bloody pulp, spitting on the corpse afterwards.
Most fans assumed because of this that Chris was also abused as a child. (This was later confirmed through Word of God)
On Supernatural, Castiel delivered one of these to Dean Winchester, when Castiel caught him attempting to surrender, which the angel considered a betrayal.
In 4x16, when Alastair unexpectedly freed himself from the devils-trap. And having been tortured by Dean for a few hours, he was quite pissed to put it mildly.
In the season 5 finale, Dean puts himself on the receiving end of such a beatdown when he refuses to leave his brother while Lucifer is possessing Sam. Lucifer takes his annoyance at the interruption of his fight with Michael out on Dean. It's... pretty ugly. And heartbreaking, because Dean just lets him do it and keeps saying "Sammy? It's OK, I'm here. I won't leave you."
In 6x13, a soulless-Sam gives one to a cop who's grown suspicious of his cover.
Lana fully intended to (and almost succeeded in) beat Chloe to death in "Delete". Mind control.
Season 10, episode 10: Earth-2 Lionel Luthor, delivers a brutal one to Clark, turning on a Green K light, and then trying to beat him to death with a belt.
In Season 5, Episode 9 of Dexter when Dexter beats Barry while telling Barry where he is punching Barry, and why it hurts so much.
In Deadwood, Charlie Utter hands out a very brutal beating to the much larger and more intimidating Woolcott, with much kicking while down. Charlie has just found out that Woolcott had murdered three people the day before; the beating was more than warranted.
GeneHunt has a special way of police investigation that usually ends in this trope. One of the most terrifying encounters is in Ashes to Ashes series 2 episode 3, where activist Adrian Mansfield is defiantly taking Gene on verbally with some astute observations about political violence while receiving a pummeling in the gents' loos.
Elliot Stabler has been known to hand these out occasionally, especially when the case involves child abuse. Notable instances include Confession in which we see the aftermath of Elliot's rampage after a pedophile posts a picture of Stabler's underage daughter on his website, and Ripped, in which Stabler beats a former partner unconscious in a courthouse bathroom after witnessing the man abuse his son.
Ripped establishes that the man had been taking steroids for an extended period of time prior to Stabler's beatdown.
It's worth noting that after Stabler beats the pedophile, Olivia supports her partner but is disturbed by his actions. Fin, who had been angry with Stabler for a few episodes, forgives him after witnessing this, marveling at his restraint. He explains to Olivia that had it been his child, he would have actually killed the pedophile. Seriously, don't mess with kids around the SVU crew.
When you consider all of the horrific sex abuse cases these men and women have worked on over the years, it's not hard to see why the SVU crew has a hard time holding back with some of the more irredeemable perps.
When Arthur catches Lancelot kissing Guinevere on Merlin he completely loses it. There's no blood or serious injury, but the audience is left in no doubt that the two would have killed each other had Merlin and Guinevere not intervened.