In Tom Clancy's stories, the good guys subscribe to this line of thinking, particularly the military, who are paraphrased at one point as believing If you find yourself in a fair fight, you didn't plan it very well.
Caine/Hari from The Acts of Caine is widely considered the best infighter alive, even after being rendered partially paraplegic. He does not fight fair, ever, and it allows him to win fights where he really should have had no chance. Illustration: right after his lowest point in Blade of Tyshalle, he escapes a dungeon cell by luring a guard in and provoking him to attack, apparently giving up the element of surprise. To recap, this is a naked and malnourished Caine, covered in his own filth, chained to the wall with his legs currently not working. The guard on the other hand is armored in chainmail, upright and well fed, and has the "chance" to draw his club and attack Caine first. After a few minutes the situation changes to that of a naked and unconscious guard in Caine's shackles while a now armed and armored Caine crawls up the dungeon steps.
In the flashbacks of Caine Black Knife, Caine describes how most armchair tacticians give advice like "Other things being equal, the advantage lies with the longer weapon" or "Other things being equal, the fighter who strikes first wins" or "Other things being equal, a big man beats a small man." He then proceeds to kill an opponent twice his size, him using a knife and the ogrillo using a spear, after the 'grill strikes first.
Caine: Get it? "Other things" are never equal.
Matt Stoverloves this trope. It even pops up in his Star Wars Expanded Universe novels; one of the best examples is a character getting into a fight he knew he would lose just to be able to track someone, so it'd be easier to anticipate the inevitably fatal fight later. The novel is Shatterpoint, BTW. This even extends to situations that aren't combat, merely minor conflicts. Such as arguments.
In the third Acts of Caine book, Caine is captured and tortured by knights of Khryl. He breaks free and mortally wounds a number of them. Later, they're healing him (Khryl is a war god, so Caine has proven his worth), but Khryl's healing only works on wounds suffered in battle. Most of the knights' wounds can't be healed, but all of Caine's can, because from his perspective the fight started the minute he saw them, while they didn't understand what was happening until half of them were dead.
Ender in Ender’s Game explains to an enemy that real soldiers don't play fair; they do whatever it takes to keep themselves alive. Ender doesn't just win; he annihilates. If he's kicking someone's ass, they won't have an ass left to be kicked when he's done. This is true from the time he's six years old and fighting (aka. Murdering) bullies in the schoolyard.
Not just Ender. This is a sentiment for every military figure in the books. Mazer Rackham tells Ender "This is war. There are no rules except what you can do to the enemy and what you can stop him from doing to you."
Bean makes a similar point to Achilles in Ender's Shadow about how real soldiers do whatever it takes to win.
"We don't give a shit about fairness here. We're soldiers. Soldiers shoot in the back, lay traps and ambushes, lie to the enemy, and outnumber the other bastard every chance they get. Your kind of murder only works among civilians. And you were too stupid, too insane, to realize that."
Staying with Orson Scott Card for a moment, in his novelisation of The Abyss the SEAL team leader, Coffey, is mentioned as having taken down a neighbourhood bully eight years his senior not in a straight-up street fight: rather, by going, lying in wait for the guy, and caving his head in with a cinderblock when the guy's back was turned. He then describes how Coffey tidies up, goes home, and never seeks any recognition of his act. On the other hand, Coffey is characterised as somewhere between a Sociopathic Hero and a monster.
Sam Vimes of Terry Pratchett's Discworld is a great believer in dirty fighting. His fighting style consists of using everything you have to hit anything you can. He calls it "artful". About the only time he's ever been delicate about the subject was when he was mentioning Nobby's "favorite kick" in front of Lady Sybil Ramkin.
His most iconic move is probably the "Vimes Elbow."
Vimes' pragmatism can be pretty well summed up by this quote:
Vimes:"And for close-up fighting, as your senior sergeant I explicitly forbid you to investigate the range of coshes, blackjacks, and brass knuckles sold by Mrs. Goodbody at No. 8 Easy Street at a range of prices and sizes to suit all pockets, and should any of you approach me privately I absolutely will not demonstrate a variety of specialist blows suitable for these useful yet tricky instruments."
Vimes' pragmatism is based entirely on one very clearly-stated principle, and it's one that serves in Real Life as well: the object isn't to score points, it's to stop the other guy hitting you as quickly as possible.
At one point he and an Assassins Guild member end up in a standoff with knives being pointed at portions of each other's anatomy that are generally considered unsporting to target. The assassin's comment that Vimes is "no gentleman" is both given and taken as a compliment.
"Make a sudden move, and neither are you."
Also Discworld: "Cohen had heard of fighting fair, and had long ago decided he wanted no part of it."
There's also one of the Silver Horde squaring off against a ninja in Interesting Times. After pretending he's getting ready to break a block of wood barehanded and making sure the ninja is watching his hands, he kicks him in the treasury and whacks him over the head with said block. Should've watched the leg, indeed.
Later on in the same book, one of the local lords shows off his Samurai by having him throw a handkerchief into the air, and slicing it cleanly in half. Cohen then throws his handkerchief into the air...and then chops off the Samurai's head as he's watching the handkerchief.
It's implied in the City Watch novels, that in the street fights of Anhk-Morpork being able to use your hands is already considered posh.
Vimes' fighting style is contrasted with that of the Marquis of Fantailler, a send-up of the Marquis de Queensbury who "wrote a set of rules for what he termed 'the noble art of fisticuffs,' which mostly consisted of a list of places where people weren't allowed to hit him. Many people were impressed with his work and later stood with noble chest out-thrust and fists balled in a spirit of manly aggression against people who hadn't read the Marquis's book but did know how to knock people senseless with a chair." A surprising number of those people's last words were something along the lines of "Stuff the bloody Marquis of Fantail-"
Vimes' opinion on Fantallier seems to have softened slightly by the time of Snuff, at least to the extent where he's prepared to offer the use of the rules when challenged to a duel. Alternately, he's offering to go easy on the poor fellow by only hitting him in certain defined placed. When they're refused, he brings this trope out in spades. "Should've accepted Fantallier", indeed.
This is a view carried (whether they learned it from him or not) by many of the watch.
Carrot, however, seems to be able to make said fighting fair work, insofar as it can be considered fighting fair for Carrot to be getting involved to begin with. In Carrot's case fighting fair might actually be considered pragmatic, what with Theory of Narrative Causality and all. Fighting fair, and generally playing fair, seem to be Carrot's form of Refuge in Audacity. Plus, who needs dirty tricks when they can cold-cock a troll with a right cross?
It didn't work in The Fifth Elephant, where Carrot gets his ass handed to him in a fistfight by a werewolf who is just as strong and fast (if not stronger and faster) as he is. Although another character cynically notes that this ultimately got his romantic competition killed off...
But Men at Arms shows that if Carrot needs you dead, there will be a foot of cold steel through you before you realize there is even to be a fight. Sometimes a sword is enough to win a gun (or gonne) fight.
Vimes' antagonist in Night Watch is Carcer, whom Vimes describes as a "bottle covey". The guy who'll take every possible way to kill you, just because he likes it, and takes advantage of the system whenever he can. In some ways Carcer is "evil Vimes", which is hinted at several times in the book.
Although he's not a viewpoint character, it's very clear that General Tacticus was a big proponent of this style of warfare; his method of command tended to not only conquer lots of territory but do it with most of his men still alive at the end, which more traditional military historians felt was somehow cheating. Vimes is, rather unsurprisingly, a fan.
It should be noted that the regular style of warfare from Tacticus's time till the time the novels take place, was basically to inflict as many "heroic casualties" on each other's army as possible. Which means to allow as many of your men to be killed by the enemy as possible. If you have more men at the end than the enemy it was a nice bonus.
Tacticus described one of the good strategies for assaulting an near-impenetrable fortress with a good supply of water and food available to the defenders: "See (that the occupants) stay there". He considers the other good strategy to be "Endeavor to be the ones inside."
Lavaeolus (Discworld's Odysseus analog) counts as well, though for different reasons, he dislikes slaughter, and so looks for every method of winning that doesn't result in it.
Rincewind will openly admit he's a coward and a rat—they survive, after all—but when cornered, his strategy is to hit his opponent with everything he can before they can realize that he doesn't know how to fight.
Rincewind actually defeated a vulnerable Eldritch Abomination that was attacking him by tackling it in a mad frenzy and targeting anything that might look like a weak point and flailing, squishing, biting, or otherwise traumatizing it.
He also ended a battle with an all-powerful reality-warping Sourcerer not with magic, but with a half-brick inna sock. Granted, it was a highly ineffective weapon, but it did end the battle.
The titular sourcerer has to be defeated and Rincewind is the only one capable of following the sourcerer through a portal. The sourcerer is just a kid that has faced lots of wizards by following orders from his father, cointained in his staff, but he only does it because they are dangerous. Cue Rincewind, inept wizzard and incapable of hurting a fly (not for lack of trying, mind you), attempting to attack him with half a brick in a sock. After asking if it's an magic sock or if this is a trick, the boy is so convinced that Rincewind is completely harmless that he refuses to follow his father's orders for the first time in his life. Technically, fighting dirty did save Rincewind's life, just not as somebody would expect it to work.
The Nac Mac Feegles are this too a tee, partly because they're fairies (of the Scottish type, ie, neglectfully dangerous at best, ranging on down to pure evil) by origin, and partly because when you're six inches high, fighting 'fair' is actually rather difficult all around. The fact that they view the Disc as a sort of heaven (ie, having been good in the past life they can let themselves go in this one) probably helps as well.
Simon Illyan, Miles's 50-something boss in the Vorkosigan Saga, is a fairly uptight but Reasonable Authority Figure. He doesn't actually get his hands dirty, he has underlings for that. When his artificial memory chip is sabotaged, and his underlings have to get him into medical treatment, though, he fights back...and he fights dirty. No one knew, because no one had ever seen him fight before.
In Ethan of Athos, Miles' protege, Elli Quinn, has to rescue a hostage, with inadequate forces and without collateral damage.
She paced back and forth like a frenzied tigress. "I'm being stampeded. I know I am. ... Q.E.D.—Quinn Eats Dirt. Gods. Don't panic, Quinn. What would Admiral Naismith do in the same situation?" She stood still, facing the wall.
Ethan envisioned diving Dendarii starfighters, waves of space-armored assault troops, ominous lumbering high-energy weapons platforms jockeying for position.
"Never do yourself," muttered Quinn, "what you can con an expert into doing for you. That's what he'd say. Tactical judo from the space magician himself."
... So she files a false report of a new infectious disease.
Lois McMaster Bujold's other series has Cazaril, an experienced soldier who is a decent swordsman but notes on many occasions that swordfighting is not nearly as useful as dirty fighting, which he is also good at.
Cazaril had to admit, the battlefields he'd been on had more resemblance to the butcher's yard than the dueling ring. But if Dy Sanda knew the desperate brutal tricks that kept a man alive on the battlefield, he'd not taught them to Teidez. (also) "I don't duel, boy. I kill as a soldier kills, which is as a butcher kills, as quickly, efficiently, and with as little risk to myself as I can arrange. If I decide you die, you will die when I choose, Where I choose, by what means I choose, and you will never see the blow coming."
Peter: "Kind of hard to kill a man when you've looked in his eyes, ain't it... [his opponent keels over with a knife in his eye] 'course, it gets easier once you've done it a couple times."
Marshal Atkins, from The Golden Age kills an alien saboteur by a) accelerating the spaceship they're on to fifty gees, immobilizing him; b) bathing the command deck with hard radiation, c) infecting it with nanobot poison, d) severing its spinal cord with a katana.
Will and Lyra from the His Dark Materials trilogy have no problems fighting dirty if this gives them an advantage. Being children going up against adults who are very willing to kill them, it's just about their only chance to win anyhow. It's mentioned that Will learned at a relatively young age that the point of fighting is to hurt the other person more than they can hurt you, not to show off; he broke a boy's arm in school and he can and has killed. He's twelve.
Mention should also go to Lyra's ability to inspire other people to follow her example, leading a rabble of confused children to pack rock-hard slushballs and "aim for the eyes".
Corwin in The Chronicles of Amber is big on this. For example, in his climactic sword duel with a powerhouse foreshadowed a book earlier, Corwin runs away, rounds a corner, throws his cloak into the other man's face as he follows, then stabs the guy while he's blind.
"Not the Winter Olympics" indeed.
His son Merlin later mocks the guy's ghost for fighting fair after defeating him again by accidentally throwing a sword at him.
This is essentially Cowin's biggest personality trait. He takes over a swords-and-sorcery kingdom with a small force carrying assault rifles. At one point he wants his son to follow him; his son declines, and so Corwin attacks him with a sword, feints around him, punches him unconscious and carries him away.
In his Wing Alek series of short stories the main character is forbidden from ever using killing to win a conflict (luckily the villains don't know that) so he uses underhanded methods to get the villains to defeat themselves.
Nicholas van Rijn from the Polesotechnic League series frequently uses sneaky methods. On one occasion, he taunts an alien prince into biting his behind; the alien prince realizes too late that human biochemistry is toxic to his people.
While he prides himself on his pure combat skill, the assassin Artemis Entreri of the Forgotten Realms novels is not above using blackmail, dirty tactics and overwhelming odds to win fights when necessary. It isn't often necessary. There is one particularly memorable scene in the The Icewind Dale Trilogy where he spits a mouthful of sewer water into Drizzt's face to gain the upper hand. Drizzt had just a few minutes earlier been wondering why Entreri was a little less talkative.
From the same series, Entreri's Drow sometimes-ally Jarlaxle is not beyond using some tricks or magic items to gain the upper hand in a fight, often to the surprise of his enemies.
In the main Drizzt novels, Drizzt met a dwarven Battlerager, a group of combat pragmatists who fly into a rage and attack like a spazzed ball of spikes, in this case their leader, Thibbledorf Pwent cops to this off the bat, citing that he's not above kicking an enemy when they're down. Usually subverted in Drizzt's case though, as he prefers to fight with a bit more honour, but its generally well understood that he'd kick an opponents ass either way.
Drizzt's weapons instructor and father Zaknafein is just as skilled as Drizzt, if not more so considering he's the one who taught Drizzt swordsmanship, but he's also very pragmatic. He uses the magical equivalent of flashbangs to temporarily blind Drow opponents and he doesn't hesitate to kick people where it hurts. He urges Drizzt to become pragmatic as well, since losing a fight means death.
Black Company, a mercenary force in the series of the same name by Glen Cook, make a living, and survive in the face of enormous odds, by fighting dirty and using every resource available to them in order to make themselves look like the baddest motherfuckers around. When it works, things look good for the Company. When it doesn't, that's when the fun begins.
Smilla Jaspersen from Miss Smilla's Feeling for Snow by Peter Hoeg has a history of winning against people much bigger and stronger than her. She stabs a man in the neck with a screwdriver when he tries to kidnap her, and topples a shelf onto a person she thinks is following her in the filing room of an office building. She also forces her stepmother to listen to her demands by pinching her in the crotch and bending her pinky finger all the way back. Apparently she's been this way all her life. She beat up a racist school bully much larger than her by finding out where he lived and ambushing him early in the morning, sending him to the hospital. When her father, a noted surgeon, tried to grab her and drag her home after she ran away at the age of twelve, she cut him with a scalpel she stole from the hospital she escaped from. When she is trapped on a ship with the vaguely psychopathic character Jakkelsen, she makes a weapon from a towel and a ball bearing, and injures him badly enough that he needs medical attention. However, she is always described as a petite and delicate woman. She is the narrator, by the way.
Possibly the best example of this trope in the 40K universe is that of Alpharius and the (Pre-Heresy) Alpha Legion. Whilst other legions had very specific ways of doing things (one legion would specialise in assault, another in defense, seigecraft etc), Alpharius decreed that his marines should master all aspects of warfare. He went even further by doing away with "inefficient" things like honour and chivalry, and often conquered entire planets through stealth and treachery.
While Alpharius did indeed preach pragmatism, he rarely practiced it. Alpharius wanted to prove himself to his elder brothers, so his tactics were usually incredibly convoluted and elaborate purely so he could show how great his men were when they pulled it off - in one case, he held off attacking a poorly defended planet so the defenders could bolster the defenses to a huge level. He won, and told his fellow primarchs that "it would be too easy" to just attack at once. A better example would be Guilliman, who favoured efficiency (he concentrated on the boring stuff like logistics and supply, knowing it would help more towards victory than cool weapons etc) or Night Haunter, who was a completely ruthless,psychoticvigilante, who led a Legion of rapists and murderers and nuked his own homeworld.
Don "Mad Dog" Slade from David Drake's Cross the Stars observes that you should only hit someone with your bare hands when you're naked and your feet are nailed to the floor.
Similar Advice is passed along to the protagonist of Star Dance by a Space Fleet Captain: "My Daddy also told me 'Only hit the soft parts with your hand. Hit the hard parts with a utensil.' "
If Repairman Jack can't beat it, he'll shoot it. Heck, he'll probably shoot it even if he can beat it - he'd rather err on the side of caution. Now, if shooting doesn't work (which is not unlikely, given some things he bumps into) things will get really funny.
The mercenary Bronn regularly uses unchivalrous tactics to win fights. When championing Tyrion in a trial by combat, he uses light armor and evades his heavily armored knight adversary until the man is exhausted. The knights in attendance find these tactics in very poor taste.
When Cersei orders Bronn to be killed, the man who does it knows that he would be no match for such an experienced killer in a sword fight. Consequently he challenges Bronn to a joust on horseback (thinking that he would lose because he would have no experience of jousting,) and plans to kill him while he's lying stunned on the ground. Unfortunately, Bronn proves himself to be a better Combat Pragmatist than him; he aims for his horse rather than him, and kills him while he's lying stunned on the ground.
Oberyn Martell uses light armor, a spear, and poison to fight the much larger, heavily-armoured Gregor Clegane. He forgets to be pragmatic where it really counts, and loses in the end, though not before fatally poisoning his opponent.
In his first scene, Loras Tyrell faces down Gregor Clegane in a joust. Gregor favours large, bad-tempered stallions, so Loras comes to the joust riding a mare in heat. Gregor's stallion did all the work for him.
Despite being a Wide-Eyed Idealist with more devotion to the ideals of chivalry than any other character in the series, Brienne of Tarth can also be very pragmatic; she defeats Loras Tyrell in a mounted melee by tackling him off his horse. In her fight with Jaime Lannister she knows that her endurance is superior, so she stays on the defensive and lets him chase her through a forest until he tires before attacking him. When he manages to disarm her, she pins him down and tries to drown him in a river—it's only a third party interrupting the fight that saves him.
Feyd-Rautha of Dune hides a needle with a paralyzing agent on his waist in his knife-fight with Paul. On top of that, he also pretends to be "shield-conditioned" (slower than he is) and leaves his right hip undefended a little too much, leading Paul to guess there's a poison needle hidden there. However, when locked in close, Paul tries to keep himself to Feyd's left only to discovers the needle is actually on his left hip and he was playing Paul very, very well.
Feyd took this approach to the Gladiatorial arena as well. When Thufir's undrugged gladiator gave Feyd and the crowd the match of a lifetime, it turned out that Feyd had put the ceremonial poison for his bout on the wrong blade, allowing him to show his cunning in front of the entire population of Harko.
Kincaid is a Psycho for Hire mercenary and all-around Combat Pragmatist. He actually gets mopey when Harry tells him he can't just level the vampires' hideout with explosives because it would kill the hostages. For a short time anyway, before he goes back to gruff and grumbling about how poor the plan is.
Harry Dresden himself. He doesn't like it, but he WILL do what it takes. A brief, and by no means comprehensive list of examples:
Up against a deranged Fae Queen, Harry, the wizard, instead of slinging his baddest spells, decides to Zerg Rush her instead. Using pixies. Armed with steel boxcutters. After which he physically pins her until she dies of a combo of blood loss and cold iron poisoning.
In other fights with magic-immune fae in the same book, he deals with an ogre by having a friend sneak up from behind and chainsaw through its knee, then setting it alight with nonmagical fire, and with charging Sidhe cavalry by tripping their horses.
When being chased by a giant magic-proof fae in a later book, he throws a pack of bottled water out the back of the car, blows it up, then pulls heat out of the area to turn the whole road behind them into an ice slick. It falls flat on its face and they get away.
When fighting fallen angel host Nicodemus, he realizes the only thing Nick is vulnerable to is the artifact which grants him invulnerability. So Harry strangles Nicodemus with it (it's conveniently in the shape of a noose).
Harry has specifically ordered his superpowered guard dog Mouse to kill more than one enemy.
Dead Beat's climax involves him creating a horrendously powerful zombieT-Rex to fight zombies.
After seeing Kincaid using incendiary shotgun rounds on vampires, he specifically starts researching the fun stuff you can do with custom shotgun ammo. Knowledge which he later puts to good use.
His standard procedure for dealing with ambushes: Run away. Fast. Anything knowingly attacking a wizard has probably come prepared. To this end, he seriously took up gymming and martial arts to improve his stamina and melee skills.
Standard procedure when his staff is taken away or runs out of magic? Start blasting what ever he is fighting with .44 rounds till it stops moving.
When taking on Cowl at the end of Dead Beat, Harry doesn't even try to fight him fairly, because he knows Cowl is a badass who'd smash him in a straight confrontation. Instead, he waits until Cowl is at the most delicately explosive point of the A God Am I spell, and then brains him over the head with his staff. Kaboom.
In "Day Off," when Darth Wannabe and company attempt to challenge him to a magical duel, Harry just pulls a gun on them. Incidentally, he keeps upgrading said sidearm through the series. This is also a special case, since killing a mortal with magic is strictly against the rules laid down by the White Council of wizards, and doing so means you can expect a visit from a surly enforcer with an enchanted sword. Harry killed his spellcasting mentornote in self defense, which made his life hell for decades; thus, whenever he engages a mortal foe, he has to use conventional means.
Harry has also found out, and demonstrated, that Groin Attacks work just as well on trolls and grendelkin as they do on humans. The fact that he did it with cold iron on the former—resulting in said troll's bits bursting into flame—let him hold off a whole bunch of them who wisely did not try to press their luck after seeing what happened to the first one.
In Ghost Story Harry interrupts the Big Bad in the middle of a villainous monologue with a blast of fire. When she voices her outrage, he does it again. When she still doesn't get the idea he hits her with a third blast. Turns out she's a bit of a pragmatist herself, luring Harry into wasting precious memories casting spells, and nearly reducing him to a mindless wraith. She can afford to take the hits better than he can afford to throw them.
In the first book, he gains the advantage against Victor Sells with a cleaning spell.
Wizards aren't the only ones who can be utterly pragmatic. The Billy Goats Gruff, while being fairytale...um, fairies, have absolutely no compunctions against using such mortal inventions as submachineguns.
Nicodemus is a Master Swordsman with 2000 years of experience, but he has no compunctions against using his shadows to control people or pulling guns in a swordfight.
He's also a Manipulative Bastard who likes to get the advantage with mind games, most memorably when he pulls an I Surrender, Suckers in Skin Game in a bid to break one of the Swords of the Cross. It works.
Winter Lady Maeve is one. When she rides into battle, with what is also a Big Damn Heroes moment, she comments she would helped sooner but "[i]f I had, it'd have been a fair fight. And I try to avoid those."
The Dangerously Genre Savvy vampire Mavra knew she would at the very least have trouble taking on Harry in a magical slugfest, so instead she uses hostages, land mines, and minions with flamethrowers. This last almost killed him. She figured out his shield only blocked physical force, not heat, so she pinned him in place and kept up with the fire until his hand was charred black. The only reason he regained the use of that hand was the wizard Healing Factor, and even then it took years.
In the Sword of Truth series, Kahlan learns about how the Mud People once slaughtered a vastly larger tribe simply by killing them everywhere except on the battlefields. In their homes, in their privies, in their beds, everywhere. Later, when confronting an army of D'Haran rebels who have sided with the Imperial Order, she puts these lessons to work. To start with, she poisons a cart of liquor and leaves it to be found by the enemy officers. Later, she leads a night raid into the enemy camp...naked, like the Celts, and butchers several of the officers remaining. This trend continues as she has her army made particular emphasis on killing physicians and other non-combatants, as killing one of them is as good as killing dozens of other soldiers who could no longer be healed by them. By the end, she has led an army of recruits to victory against a battle-hardened veteran force ten times its size.
Later, during the fighting retreat as the Imperial Order in its millions finally invades the New World, Kahlan increases her pragmatism by an order of magnitude. After the D'Haran army is handily defeated in a stand-up fight, she takes charge and spends the better part of a year using hit-and-run guerilla tactics to grind down the Order's army by hundreds of thousands. In her most impressive feat, she she uses a barrel of powdered glass and scatters it in front of an advancing enemy force, killing thousands from lung infections and causing tens of thousands to go blind.
Kris, the Action Girl star of Mike Shepherd's Kris Longknife series. Shepherd mentioned that while most marines had to be trained out of notions of fighting fair, she took to dirty fighting like a duck to water.
The Third Rule of the bodyguard school called Matador Villa in Steve Perry's Matador series is: "There are no rules in a fight involving death."
Anita Blake isn't at all averse to this, especially considering she's usually up against vampires, shapechangers or worse but she pales compared to Edward, famous for using a flamethrower against some vamps.
This shows up all the time in Mercedes Lackey's work, especially her Velgarth novels. Fighting instructors, as opposed to fencing masters, constantly emphasise to their students that there's no such thing as "unfair" or "dishonourable" tactics in a real fight. Fencing matches and the like are a different thing entirely.
The Dorsai do believe in thinking outside the box. However, they would never, ever, violate the "Mercenaries Code" (which is something like the Geneva Conventions). When one person asked one of the Dorsai commanders if he had ever shot prisoners, the commander got quite threatening about the idea that he would ever do such a thing.
Mike Z. Williamson's Freehold, especially the Black Ops. Think Improvised Weapons Of Mass Destruction.
In Yoda: Dark Rendezvous, this is how Weak, but Skilled Padawan Scout wins an Initiate tournament. She takes advantage of a lot of things: that some of her opponents are unwilling to seriously hurt her, that she can throw things in people's faces, that There Ain't No Rule against leaving the ring or ducking behind the referee, and especially the fact that in the tournament, lightsabers are turned down and won't cut through her if she grabs the blade. Notably, she never outright breaks a written rule, just unsaid ones.
The Star Wars Expanded Universe is RIFE with this, especially with certain authors, such as Stackpole and Allston (who wrote Starfighters above.) In the X-Wing Series, both Rogue and Wraith Squadrons are completely happy to use any unfair and probably illegal methods they can think of, including pretending to be the enemy, flying false flags, and acts of piracy. Note that in Real Life, all three of those are HIGHLY illegal. Hell, Wraith Squadron was BUILT on this, using random misfits and Special Forces soldiers as pilots specifically so they wouldn't fly and fight like pilots.
In Real Life pretending to be the enemy and flying false flags is illegal IF you open fire while pretending to be the enemy or flying false flags. Change to your own colors, flags, uniforms and IFF beacons befour shooting and you are clear of problems (legal ones). Piracy is solved by Letter of marque that names a Enemy, acts of piracy against ENEMY (with whom you are at war) shiping is legal. Wraith Squadron was given permission fron Command to carry out acts of piracy against Empire forces and goverments that suport the Empire.
Mara Jade is particularly fond of this, especially before she firmly joins the good guys.
The novelization of Revenge of the Sith offers a better explanation (that is to say, an explanation) of how Palpatine killed three of the best swordsmen in the galaxy without breaking a sweat. When the Jedi Masters came to arrest him, he pretended to be a helpless politician, terrified of four armed men threatening him for no reason. The moment their certainty faltered, he was across the room and one's head was bouncing off the floor, while another staggered with a hole drilled through his forehead. He may be old, but he's a Master of the Dark Side.
Partially because she's untrained but mostly because she's her, Sirantha Jax of The Sirantha Jax Series will use any means to win — fighting dirty, crazy tactics, you name it.
Alanna/Alan from Song of the Lioness is being abused by a bully. What does she do? She goes into the city, and has her friend George and his men teach her street fighting. Alanna and the bully fight, and Alanna wins. Of course, everything that she does goes against the code of conduct for the boys, but...
Keladry from Protector of the Small is an adherent of this too. When she's faced with uneven odds in the first pages of the first book, she grabs a big stick as an "equalizer" and hits all the boys in their muscles and belly. When punched in the stomach by Joren's gang, she deliberately aims the resulting barf at one of her opponents.
In Chris Roberson's Imperial Fists novel Sons of Dorn'', Jean-Robur learns to fight like this in his first battle, stabbing a foe In the Back.
Dragaera: Vlad grew up in a bad part of town as a victim of Fantastic Racism before clawing his way up to a mid-level position in the Jhereg as an assassin. This, along with the fact that most of the people he's fighting are bigger and stronger than him, has led him to become the kind of guy whose standard tactics involve having his poisonous-miniature-dragon familiar fly into people's faces to distract them.
Backfires on him once, as well. On their way into the Paths of the Dead, Vlad Taltos and Morrolan are forced to face a group of Dragonlords, one at a time, in single combat. Vlad throws a knife at his opponent while the latter is waiting for him to draw his sword, which makes the Dragons angry enough to attack them all at once instead.
Sherlock Holmes is a weird case. Holmes himself has a general Screw The Rules attitude, but he completely averts this trope as he usually prefers to fight fair in hand to hand combat. Watson, the veteran of Afganistan, is far more conventional, only breaking society's rules when there are lives at stake, but if you ever come down to Baker Street looking for a piece of him or his homeboy he will grab a chair, or poker, or whatever and bust your head open with it before you even get to throw a punch.
Garren in the Farsala Trilogy fits this trope, despite being the villain. In a duel meant to decide the fate of Farsala, he calls in his entire army when the odds turn against him. Of all the characters, he's one of the few who really understands how to get the job done. That doesn't mean we have to like him.
He does this twice. In the first book, when the king challenges him to a one on one duel on the battlefield to end the war quickly, what does he do? He simply orders several archers to shoot him while he stood there without attacking.
The second time is the one mentioned above. When he has yet another duel to determine the kingdom's fate, he actually begins to lose...and so he orders the exact same thing on the teenager who was beating him. This was going a bit too far, however, because the main female protagonist completely destroys him with a bolt of lightning afterwards.
On a larger scale, Garren's combat pragmatism causes him to win the battles but lose the war - while tactics like using hostages as shields, disregarding the challenge circle, using peasant conscripts as cannon fodder, and torturing a prisoner make life a lot harder for the protagonists, they also undermine the support of his subordinates and secure popular support for the resistance.
Valentinian from the Belisarius Series is a vicious bastard who compensates for his (relative) lack of height and bulk compared to some of the other badasses in the series by taking advantage of his lightning fast reflexes to help him pull off every dirty trick in the book. He's so good at it that late in the series he trains a twelve year old boy well enough that the kid can take out multiple professional soldiers on his own. He loses one fight in the series, against the legendary Rana Sanga, specifically because he steps away from this trope for once (he had Sanga wounded and could have picked away at him and bled him to death while staying out of reach, but chose to try to finish the fight honorably and had his sword (and skull) broken as a result). He survives and avoids doing anything that stupid ever again.
On a larger scale, Belisarius himself. Facing an army too large to fight head-on? Give 'em a good swift kick in the logistics.
Kirth Gersen from Jack Vance's The Demon Princes cycle. At one point during a Blood Sport, he and one other player face off against The Dragon. Gersen has a number of cheating options available. What does he do? Make a deal with the other player to split the prize, and team up.
Arthur Dent has a moment of Pacifist Pragmatism in The Hitchhiker's Guide to the Galaxy. He finds Trillian and Thor canoodling at a party, and challenges the later to step outside for a fight. The party was taking place in an airborne building. This version of Thor can't fly. Of course, there might've been a porch outside, but Arthur locks the door when he leaves and suggests everyone nip out the back. It later turned out he survived.
Present in The Pyrates in the form of Colonel Thomas Blood, skilled swordsman and master shin-kicker. His dirty fighting is enough to let him keep up with classical master (and deliberate Canon Sue) Long Ben Avery, despite being slower, weaker, and far less fit. Also averted by pirate swordmaster Black Bilbo:
Avery, on t'other hand, is a genius, as we know, and younger and fitter — but then again, Bilbo has the experience, and knows lots of tricks — but curiously enough, black scoundrel though he is, the thought of using them never crosses his mind.
Don Quixote: Alonso Quixano admires famous Knight Bernardo del Carpio because he defeated Roldan (in an alternative legend to the Song of Roland) because, instead of attacking Roldan the Enchanted with a sword, Bernardo just strangled him. Part I, Chapter 1:
Quite a few of the characters in the Honorverse. At one point, Honor has to meet a pirate warlord in person to arrange the release of hostages he is holding. Knowing that he will scan her for energy weapons, she simply brings along a semi-automatic handgun (of a model that went out of style millenia before the story takes place.) She plugs his goons and captures the warlord once they let their guard down.
This is shown to rather gruesome effect in the thwarting of an assassination attempt during ''The Honor of the Queen''. As the security cameras picked up the entire battle-cum-massacre, Honor and (especially) Nimitz completely shredding the assassins and nearly getting killed in the process ends up broadcast across the entire planetary news service, redefining her rather handily in the minds of almost any Grayson.
In the novel Party Line by A. Bates the male protagonist goes to a self-defense class, the instructor emphatically tells the students to go for the eyes, ears, throat, etc. When the protagonist happens upon a kidnapper later, he does precisely that. When he wakes up, he finds out that it didn't work because the kidnapper was the self-defense instructor.
James Patterson's Alex Cross novel Kiss the Girls has a woman who takes self-defense classes, with the Groin Attack recommended. When Casanova abducts her, she kicks him in the nuts. Unfortunately, Casanova was wearing protection. Because he had been watching her go to her self-defense classes.
From the same author as The Dresden Files above, Codex Alera is set in a land where everyone has access to what are basically elemental Pokémon, and the main character is the one kid who doesn't. As a result, he's had to rely on his wits where most people use brute force. For example, salt dispels wind "furies", wild or tame. So he specifically carries around rock salt should he encounter some wild ones, and gives his uncle the idea to use rock-salt arrowheads, which are very useful against aerial attackers using wind furies to fly. By the fifth book, he's pretty well known for winning apparently hopeless fights.
The Vord Queen, the Big Bad of the series, is even more of a pragmatist than Tavi. She expresses her disappointment over the fact that she can't kill refugees because soldiers are covering their escape. When it's pointed out that every able man is already fighting, the Queen points out that the elderly civilians can bring experience, the women can bear young, and the children will grow up to be her enemies. That clears "pragmatism" and goes straight into "sociopathy".
Skulduggery Pleasant has three usual weapons; his fists, a fire spell, and his revolver. Given the heavy The Dresden Files influence, a good portion of the magical community seems to have absolutely no problem using firearms and hand-to-hand whatsoever. One exchange came from the second book, however, between Baron Vengeous and Skulduggery:
Baron Vengeous: "...only a heathen would bring a gun to a swordfight."
Skulduggery: "And only a moron would bring a sword to a gun fight."
In The Spellsong Cycle, Ashtaar Ashtarr notes that Secca is one of the most dangerous people in Erde precisely because she is this, borne of her hatred of fighting and willingness to do anything to end a fight as expeditiously as possible. Her mentor Anna did that, too.
In the Dale Brown novel Executive Intent, the Chinese are this in their attack on Mogadishu. Some guy firing on their troops from a building? Most forces would try to storm the building and get into risky room clearing. Screw that. They level the whole damn building. Doesn't matter if you're a militiaman/pirate/gangster or really just a civilian - you make the mistake of gathering in a group that could be remotely construed as a regrouping squad, they'll mow you all down and let Chairman Mao sort out the dead.
In the Young Bond series, there is a character called "Red" Kelly who teaches James Bond (yes the very same only, well, younger) that fights don't have rules. He says that " No such thing as fighting dirty, really, Jimmy. There's just fighting to win. use whatever you like, you can forget about rules..."
The eponymous protagonist of the Sandokan series and his best friend Yanez are this. While most of the times this manifests in ambushes and the normal tricks of the middle 19th century pirate of the Indian Ocean, they have sometimes gone overboard, with Sandokan setting the record for the foulest act of Combat Pragmatist in Yanez's Revenge by using cholera against the enemy of the novel (a twenty thousands-strong army of Indian outcasts armed with muzzle-loading guns and antiquated artillery) and deploying a dozen early machine guns to give the cholera time to make the enemies literally shit themselves to death.
Sandokan is also at the receiving end of the first act of the series: in the first novel Sandokan and two prahos (small sailships) worth of pirates are fighting a British cruiser, and, knowing they're hopelessly outgunned, start paddling to board the enemy ship... That uses her steam propulsion to move away at the last moment, provoking the pirates into screaming insults and obscenities until the cruiser resumes firing.
In Harry Potter and the Deathly Hallows, Professor Slughorn and the Slytherin students leave the school before the start of the Battle of Hogwarts. However, Slughorn and several Slytherins return later to join the fight, after having gathered reinforcements from the families of those who stayed to defend the castle.
David Gemmell characters, by and large, tend to favour the policy that the best opponent is a dead one, and that rules that get in the way are best ignored. It's even a plot point in Hero in the Shadows when Waylander chooses to fight in a semi-honourable but still brutal duel rather than just nailing the guy with a crossbow bolt.
In Trainspotting, the feared barroom brawler Francis Begbie is known to carry a variety of home-made weapons about him, such as sharpened knitting needles. Renton suspects that he's actually not a very good fighter in a "square go."
In the beginning of the first Night Huntress book, Cat complains that she would have killed Bones if he hadn't sucker-punched her, to which he laughs and lectures her that fighting dirty is the only way to fight. She takes the lesson to heart, and eventually teaches it to her subordinates in the military.
Lampshaded in John Varley’s Golden Globe: “If you must shoot somebody, aim for a spot right between the shoulder blades.” As the villain didn’t turn her back to Sparky, he shoots her through the door, looking through the peephole.
The Justicar, the main character from the three Dungeons & Dragons novels White Plume Mountain, Descent Into the Depths of the Earth, and 'Queen of the Demonweb Pits lives by this trope. He attacks from ambush whenever possible, hits below the belt, and his (often repeated) personal view on combat is "if they hit back you did something wrong."
Parker, the central character in a series of novels by Richard Stark, will do whatever it takes to win a fight. The idea of "fighting fair" would never cross his mind.
Every Lensman has a completely detailed knowledge of all the lethal tricks of foul combat known to all the dirty fighters of ten thousand planets for twice ten thousand years.
In Spellbound, the second book of The Grimnoir Chronicles, Sharpes, a heavyweight boxer decides to have fun beating up Heinrich, a currently-de-powered wizard. Unfortunately for him, Heinreich had grown up in a zombie-filled city and is used to fighting above his weight class. Heinrich opens with a series of groin shots and builds from there.
Penny's mother in Please Don't Tell My Parents I'm A Supervillain, to the point that most criminals will surrender instead of fighting her, despite the fact that she has no actual powers. One villain, the Bull, tells a story of how she fought him. She stuffed sand in his eyes, nose, and ears, tricked him into punching a telephone pole and electrocuting himself, and then hit him with a bus.