Choujin Sensen: The Experts are people with plenty of battle experience to fight on parr with their superpowered opponents. The Experts will methodically destroy their foes whether it be disarming their abilities or crippling their bodies.
The "scissor" move of his Rock Scissors 'n' Paper technique was eye-gouging and sometimes he'd use this technique by pretending to use one move and instead using another one (shouting "paper" and using "rock" instead, for example). He also resisted Tien's Solar Flare technique by wearing Master Roshi's sunglasses.
He escapes from being strangled by Frieza by biting the latter's tail. He also bites Kid Buu when he was fighting him as a Super Saiyan 3, but this time it was mostly played for comedy (Kid Buu bites him first). He also bit King Piccolo's thumb in their first fight.
Before then, he planned to defeat his brother Raditz by grabbing his tail.
Invokes the trope again during his fight with Recoome where he defeats Recoome with a single elbow to the stomach, but did it while Recoome was powering up to perform a technique. Goku even lampshades this after the fight is over:
Goku: I saw an opening that screamed attack... so I did.
He punches Jeice square in the nose while he was still talking.
Vegeta has no problem with dirty fighting either.
He notably throws sand in Zarbon's eyes to temporarily blind him, after which he punches him in the back, breaking his armour.
Vegeta defeats Guldo when the latter is distracted with attempting to kill Krilin and Gohan. Guldo blames Vegeta of cheating but Vegeta has a proper response:
Vegeta: There's no such thing as fair or unfair in battle. There is only victory or, in your case, defeat.
He kills two of the Ginyu Force members while they're unable to defend themselves.
King Piccolo is also this. He immediately kills Chiaotzu when he tries to sabotage King Piccolo's quest for immortality by making his wish to Shenron before Piccolo does. He also checks Goku's pulse before confirming he is dead in their first battle. He's a Magnificent Bastard for a reason and the only villain to ever outright win.
Piccolo penetrates Goku with his Breath Weapon when the latter is distracted by the thought of victory, right before the Combat Commentator could say "10".
Future Trunks, bless him, he tries to fight according to "common sense". He does have a sense of honor, but that's for friendly sparring matches or tournament bouts only; when it comes to saving innocent lives, he'll do whatever works. Unfortunately for him, he's in a Shōnen series. That said, when he is stronger than his opponent, it does not last long. Future Trunks is not interested in a fair fight, holding back, or challenges. This is justified as a byproduct of the Bad Future he grew up in. It's seen clearly against Frieza. Instead of letting him power up to 100% like Goku did, he cut him in half the minute he is distracted. (In the manga at least.)
He's also the only who thinks to attack Cell during his Transformation Sequence. It doesn't work (apparently transforming generates a heck of ki barrier), but points for trying.
Krillin... initially. It's about the only thing he could do to keep in the frontlines longer than any of the other humans in Z. Notably, however, he never employs the Solar Flare/Destructo Disk combo that could've probably killed any major villain up until Cell. Probably because the Destructo Disk is implied to be very hard to control.
Jagi made a career out of doing this. Be it spitting needles, using a gun, or making a hole in an oil tanker and lighting the leaking oil on fire with him on top of said tanker. This translates into the video game, in which his move set involves using a shotgun, setting oil barrels and gasoline puddles on fire, throwing needles, chaining his opponent to a cinder block, using pillars and random junk as weapons, pistol-whipping, and the aforementioned oil tanker trick.
Jackal was no novice at this either. His primary offense was throwing Dynamite, with concealed blades and other such dirty tricks, unlike most people, he did not receive martial training or any superpower, yet he still poses as a serious threat to Kenshiro by manipulating the environment and the people around him.
Yuda takes the cake. Rei, a superior opponent, is out for his blood but is set to die in three days? Easy, he tells his head subordinate he's leaving for another town specifically to do this, waits for a pissed Kenshiro to torture him into saying in which town he's hiding in, and as soon as Kenshiro and Rei leave he calmly walks back at home and asks if his subordinate really expected him to tell him where he actually was going (he had not left the town at all, he was just hiding across the street). And when Rei managed to prolong his life indefinitely, he accepts the challenge... And has his subordinates blow up a dam to flood the place and impair Rei's mobility, as Rei needed to touch his enemy to kill him but Yuda could easily but slowly cut him from distance (and the water actually increased the power of the attack). The only reasons Rei won was that Yuda interrupted that attack to brag before using a similar but stronger one, giving Rei the time to use his hands to push on the water and jump, and, after that, Yuda froze up seeing the beauty of Rei's attack.
Also, Kenshiro himself. He's a trained assassin, and, when the situation requires it, he's not above to grab the largest rock in the place and throw it at the enemy or use whatever he can, and at one point starts wearing a weighed glove to add some power to his punches (and to tribute the previous owner of said glove, an ally of his).
All Hokuto and Nanto practitioners, with such highlights as a technique to grab an enemy arrow and throw it back without looking and techniques specifically made to sneak up on someone and detecting someone trying this. In fact, the only reason Hokuto and Nanto practitioners apart from Jagi and Yuda aren't obviously this is that they usually find themselves in situations where they lack something to bash the enemy with, it could cause collateral damage, or are fighting an opponent that is so good that normal tricks are next to useless. In fact, the above-mentioned Jagi's reliance on those tricks is seen as him trying and failing to compensate for his own weakness (the needle-spitting trick was pulled on Kenshiro during a spar. At the same time, Kenshiro mock-performed a lethal move on him), and during their fight Kenshiro actually chastised Shin when a Mook tried to sneak up on him not for being underhanded but for actually expecting it would work (Yuda, on the other hand, is so good that his tricks work even on opponents that would usually not be even slowed down).
Nanoha Takamachi has no problem shooting people in the back, magically freezing them so they can't resist her attacks, et cetera. It's worth noting that every dirty tactic she uses on someone else is a tactic that was once used on her. (And her attacks tend to be non-lethal anyway, so she has almost no worries about killing her rival in battle.)
Teana Lanster uses illusions to trick her opponents and she tends to attack them on certain weak spots, such as the occiput or the chin, or simply from behind.
Deed tends to take her enemies by surprise, often by jumping out to suddenly attack, attacking from behind, or Playing Possum getting up from supposedly being unconscious for a sneak attack.
Chantez Arpinion being a Teana expy also uses illusionary doppelgängers and is dirty enough to lie to the opponent about the number of said doppelgängers or that she's even using doppelgängers to begin with.
The very first thing we see Curren do on-screen is shank HayateIn the Back.
Most of Go Nagai's characters have absolutely no trouble using cheap, dirty tricks to win their fights and nowehere they show they know of, feel concerned about or bound to rules of fair play and sportmanship. Given what is in stake when they fight, it is unsurprising. Several examples are:
Ryoma Hayato, Musashi and Benkei from Getter Robo. Hayato is a particularly prominent example. If the enemy is holding hostages, he exhorts his teammates to disregard the hostages and keep fighting, arguing everybody will die if they do not.
Honey Kisaragi from Cutey Honey. In one occasion Honey even stripped naked to distract a foe with the light of how she stripped just long enough to kick him in a fire (the foe died when his flamethrower exploded, just as planned).
Section 9 from Ghost in the Shell is probably one of the least heroic teams of protagonist police officers. As they are fighting terrorism and organized crime, and the government and judical system is completely corrupt, they have the policy to kill any armed suspects on sight and only try to make arrests when it's relatively safe and any other mission objectives have been secured.
Granted, this is a future in which a good portion of humanity is augmented and shooting a person ain't what it used to be, but they're still aiming for the weak spots more than usual.
The one thing you'll never have to ask Akaya Koudai is, "Why don't you justshoot him?" 'cuz that's likely to be his first course of action. At the start of chapter 34, he helped saved Gen by using his Maken's hypnosis ability to conceal his presence, then shot two of his opponents. In the brief time it took them to realize they were under attack, it was already over.
Mobile Suit Gundam: As the original bearer of the White Devil name, Amuro Ray is a textbook example, basically doing anything and everything in his power to kill his enemy. He has no qualms shooting distracted opponents, sacrificing various armaments, and ambushing opponents. He even takes this to the logical conclusion, using the Gundam as a decoy in order to rush to the enemy cockpit and take out Char.
Char was no slouch either: the first thing he did after realizing that his Zaku's standard weapons were useless against the Gundam's armour was to repeatly kick the Gundam over the cockpit to stun the pilot, and, after being forced to retreat, he brought mecha-sized axes that could damage the Gundam and an anti-ship rocket launcher (good enough to pierce the armour of those five batteships at Loum, good enough to kill the Gundam). His other tactics include force the Gundam to re-enter atmosphere out of the White Base (the only reason it didn't work was that the designer had equipped the Gundam for just that), use strategically placed bombs to drive an enemy battleship to block the hangar of Luna II, and infiltrate the headquarters of the Federation to destroy the new mobile suits before they could be deployed.
The cake for the original series goes to both a group of Zeon soldiers who nearly destroyed the Gundam by jumping it on jetpacks and jetbikes and place demolition charges (the Gundam survived because they had only time bombs, and the crew managed to defuse them just in time), and M'quve, who used the same trick on much larger scale (he was the supreme commander of the Zeon invasion force, he had the resources) to down the White Base.
One of the dirtiest and most creative fighters in the franchise is the protagonist of Mobile Suit Victory Gundam, a shy, kind-hearted little thirteen-year-old boy named Uso Evin. In addition to using all of Amuro's tricks (see above) with considerable flair, he has several of his own devising, with a particular favourite (later adopted by the rest of the League Militaire) being detaching his Combining Mecha's lower body and turning it into a giant kinetic warhead.
Mobile Suit Gundam Wing: In the final story arc, Zechs Merquise (previously a Worthy Opponent and thus a major subverter of this trope) has become the leader of the space rebel group White Fang. Treize Khushrenada, leader of the Earth's military, proposes a one-on-one duel in order to decide the conflict. Zechs' response? Fire his space fortess's Wave Motion Gun, saying that a simple duel won't resolve the underlying causes of the war (for the record, it misses - but only because of external intervention).
Mobile Suit Gundam SEED Destiny: Shinn Asuka...when he's not too pissed off to think straight. When he fights calmly, he often uses clever improvised attacks (for example, using an enemy mobile suit with a breached reactor as a giant grenade to take out an enemy Wave Motion Gun that was shielded against beam weapons, splitting apart his Gundam mid-flight (Getter Robo style) to dodge attacks, or throwing away his fancy beam-reflecting shield...in order to bounce his beam rifle shots off it and hit the enemy from an unexpected direction). Unfortunately, he has led such a traumatic life and has such poor anger management skills that he gets pissed off very easily, and basically turns into a Leeroy Jenkins. One of the few instances where being Hot-Blooded actively undermines a mecha pilot.
Mobile Suit Gundam AGE: The UE may have set the record for combat pragmatism in Gundam. They camp enemy hangars, shoot down supply crates, don't hesitate in killing off defenseless foes, promote infighting in their enemies, back off when faced with superior opposition... their effectiveness in battle is as much due to their intelligence as their advanced technology.
Second generation Flit doesn't care about beating his opponents in mobile suits, as demonstrated when he responded to Desil's challenge by unleashing a full AA barrage from his battleship. "This is war. The manner in which I defeat you is meaningless."
Third Generation Asemu aka Captain Ash also qualifies. His pirate-themed Gundam is outfitted with some dirty tricks on its sleeve, like anchors charged with electricity to fry enemy mobile suits (and their pilots inside) and a floodlight mounted on its chest to blind his opponents.
Mikazuki and Akihiro of Mobile Suit Gundam: Iron-Blooded Orphans fight to survive and crush their enemies, they wouldn't question the so-called codes of honor of Gjallarhorn and simply shoot them when they are talking, crushing them when they are outside the cockpit. And should you wronged them or killed any of their brothers, Mika would shred you into piece without caring who you are. One memorable moment late in the first season saw a group of Gjallarhorn pilots doing a sort of role call mid-battle...and Akihiro shoots one of them before he can finish his sentence.
Naruto has Uchiha Itachi, who uses his tactical insight and cunning nature to apply everything in his favour. This becomes most obvious after his resurrection, where he allows a resurrected Nagato To curb stomp Naruto and B simultaneously, so he can set up an ambush that grant them the advantage against Nagato. Similarly, he uses Sasuke's presence to allow him some leeway for sacrificial attacks and strategies. He allows stalagmites/tites to impale him and later is cut in half, knowing that his edo tensei body can overcome this and Sasuke is there to back him up. He later on readily sacrifices one of his eyes, knowing that his goal will send him back to the afterlife anyway.
Asuka Kuronari. Sure, she's a ninja, but she proves almost suicidally determined to come out on top against Kyoichi Kunugi, who has her hopelessly outclassed throughout the fight. That is, until she starts crying her eyes out, telling him her pathetic life's story and deploying a smoke bomb while he's distracted, allowing her compatriot Xiaoxing the chance to attack him.
Xiaoxing herself, as well; her entire fighting style revolves around using Instant Knots to tie her opponent up, thereby incapacitating them.
Kunugi often uses the Breaking Lecture to disarm opponents (figuratively speaking) while confusing them with illusions and violently seizing every opening in their defense.
Ranma Saotome does this whenever he battles an opponent that is clearly more powerful than him. When facing his rival Ryoga, who'd been powered up by the Mark of the Gods, he resorted to using the "Saotome Desperation Techniques", which were basically just creative ways to make his opponent look away from him so could attack them while they were distracted ("What's that behind you?!", "Look, there's 500 yen on the ground!", etc.). When he was getting his butt kicked by prince Herb, a man with an irrational hatred of breasts (due to be being cursed by a naked girl while he was distracted by her boobs), Ranma repeatedly flashed his breasts at him, until the guy was so overwhelmed with anger that his accuracy was shot to heck. The man is the heir to the Saotome Anything-Goes School of Martial Arts for a reason.
Then there is the a twist on this with the "Saotome Ultimate Desperation Technique: Crouch of the Wild Tiger" which is getting on your knees and saying "I'm sorry" constantly. Lampshaded by Cologne on how stupid it is till Akane shows up and it gets used well.
Cologne herself. In the manga she once had a battle with Ranma in the sea. What did she use to stand on the water? A great white shark.
KODACHI. KUNO. She is, without a doubt, the dirtiest fighter of the series. She has weapons that can instantly turn lethal at will. She'll use her ribbon to grab and immobilize her opponent or throw objects at him/her. She bends the rules like mad and uses cheap tricks such as trying to shake Ranma's hand with tacks between her fingers and paralysis gas and pills in food and flowers, trying to put her opponents at a disadvantage even before a match. She will do anything it takes to win and sink lower than the Titanic to achieve victory.
According to Kodachi herself, cheating is an inherent part of her style, and if you cripple an opponent before an official match she was obviously not good enough (and, to be fair, after the first attempt she didn't attack Akane again except by reflex: she was going to meet Ranma, and Akane was there...). Given that, when she fought Female!Ranma in an official match her use of her brother as a weapon was allowed, she may be right.
Let's face it, every single martial artist worth his salt is one here. The exception is Kuno... And even he will find a loophole to fight dirty.
Part 2 Big Bad Cars also quickly proves that, unlike Noble Demon Wham, he doesn't give two shits about honorable fighting when he goes up against Lisa Lisa under the pretense of a duel, only to use a vampire Mook as a body double to distract her long enough to skewer her from behind.
Prosciutto from Part 5. While other Stand users tend to rely almost entirely on their Stands, Prosciutto also carries a gun with him on top of it which lets him nearly kill Mista during their fight (there are other gunslinger stand users, Mista included, but their Stands are tailor-made to enhance their marksmanship, while Prosciutto just carries a gun as a backup weapon.)
Askeladd in Vinland Saga is more than willing to just have his men stick an opponent full of arrows then fight him one on one.
Thorgrimm as well.
Kiritsugu Emiya of Fate/zero is basically revealed to be the god of combat pragmatists, if said god was injected with extra pragmatism steroids. He wants to save people, but came to understand that saving some means sacrificing others and decided that at least he could save the many by sacrificing the few, and became an expert in killing mages with extremely low-blow tactics. This leads to personality conflicts with the "knight of the sword", Saber, who he summoned as a servant in the Fourth Holy Grail War and who greatly believes in fighting in an upright fashion.
One Crowning Moment of Awesome of Kiritsugu involved using C4 explosives to bring down a magically defended building. Practical indeed. And he considered this worryingly soft of himself because he put in a bomb threat to get the civilians out about fifteen minutes before. Even though his target would most likely never even get said warning from the hotel staff let alone bother to think it was dangerous.
This is the raison d'être of the Assassin class. They're unfit for fighting so they make extensive use of their Presence Concealmentskill while targeting Masters instead of their Servants.
Lone Wolf and Cub's Ogami Itto has been known to kill his quarries with a sword... or spears or naginatas... or his own bare hands... or any other damn thing within his reach, from a wooden board split in two with a knife hand strike to a proto-gatling gun.
It's lampshaded heavily how dirty he fights. If he's facing someone with similar skills, you can expect him to use some kind of trick. This includes throwing his sword (quite dishonorable and unthinkable for a samurai) and using his own and only child as a bait.
Of course, Yagyu Retsudo is equally pragmatic either in battlefield as in politics. He just has to do it undercover in order to not losing face (which Ogami also uses in his advantage).
Saito Hajime in Rurouni Kenshin, who explains this to an idealistic youngster by stating that in a real fight, there is no such thing as fair.
In the Jinchu arc flashback, Kenshin relates how Tatsumi, the leader of a group sent to kill Himura Battosai, lured him into a forest that smothered his sixth sense, and then threw his minions at him to deprive him of his other senses. All so he could finish Kenshin off in a weakened state.
Tatsumi: Do you think I'm a coward? There's nothing wrong with that. This is the strongest weapon of a seasoned warrior...it is called "cunning."
Rakan of Mahou Sensei Negima! occasionally classifies. Lifting skirts up to flee from a fake dimension, plus stealing the girl's panties certainly does.
Upon arrival to the Magic World, Negi senses a familiar hostile presence (revealed to be Fate Averruncus). Fate, upon realizing he has been detected, rather than simply showing himself instead opts to attack with a Stone Spear from the shadows striking Negi in the back and seriously injuring him. After a fight Fate then proceeds to scatter Negi and his companions around the magical world by use of Forced Teleportation.
Mana Tatsumiya: When in battle there is no such thing as holding back my techniques.
Honorable mention must go to Gantz's Masaru Kato. When threatened by a much larger bruiser what does he do? He catches the bastard with his pants down (quite literally — he ambushed him on a toilet) and beats him to kingdom come. Can't get more pragmatic than that.
Berserk's Guts is no honorable swordsman. He's willing to let opponents beat him up so that he can blast them with his Arm Cannon at point-blank range, bites an opponent's sword in one fight after Griffith jumps on his sword, and actually prefers to kill opponents with long-ranged weapons rather than engaging in melee combat.
And this doesn't even mention things like his willingness to take innocents hostage if he thinks that it'll give him an advantage, which fits the concept of "fighting dirty" much better than anything mentioned there. At one point, he uses a small child, hanging by his clothes on his sword, as bait to distract a swarm of vicious, homicidal "fairies" into chasing him into a barn where he blows them up. The kid doesn't get hurt, either.
At one point, Guts is training Isidoro (a young boy who seems to believe Berserk is a SHONEN manga) and Isidoro nearly pulls off a sneaky attack using his speed and smaller size to his advantage. Isidoro berates himself for trying something so dishonorable, but Guts praises the pragmatism of the attack, telling Isidoro that he needs to use every advantage he has.
Vagabond has Miyamoto Musashi who ironically embodies this trope more so than merely being a swordsman; more specifically he is described as "flexible and unfettered," taking the opportunity as it comes. Notably demonstrated in fighting the Yoshioka at Ichijouji, as he takes the opportunity of showing up an hour early and from the mountains instead of the road, allowing him to severely wound their leader right at the beginning. He may have defeated Inshun, Shishido Baiken (his Dual Wielding was to overcome the different mechanics involved in the chain and sickle), and the Yoshioka brothers (defeating the second brother's attempt to clinch and set up a killing blow by gutting him with his own wakizashi on instinct), but this is ''the'' defining fight for him. It's also a defining fight for the Yoshioka as they try and almost succeed at this, but can't quite "reach that far" and he mostly succeeds at fending off their attempts. (The closest they ever come to actually killing Musashi is when Nanpo Yoichibe tackles him to the ground and holds him down, but it fails since his cohorts hesitate to simply stab Musashi to death through Yoichibe.)
In general the Yoshioka leadership failed to prepare themselves and their followers for the essential fact that instead of dueling it was kill-or-be-killed.
And it isn't limited to combat per se. In an early Tournament Arc he proceeds to gather as much dirt as possible on his opponents' private lives, then blackmails them into throwing the match. A solid case could be made for Shamo being a Deconstruction of such character type as Ryo is reviled both by other characters and majority of readers.
In Kenichi: The Mightiest Disciple, they take the titular character to visit another martial artists to learn 'tactics' which amounts to pragmatic fighting. The lesson doesn't really take.
Also, Fake!Loki counts as well — during his fight with Kenichi, he pulled a tazer, among other nasty tricks (Although they didn't work well at all). The real one is even more so.
"An honest person is another name for a fool!"
Slayers has Xelloss. Gaav states that Xelloss's specialty is to attack someone in the physical plane from the astral plane, which would best be characterized as a sneak attack (as Gaav demonstrates). Also, in Xelloss's battle against Valgaav he uses some very dirty tricks, one of the most notable being when a stray blast put a team mate in danger (Filia), he rescues her then immediately drops her on Valgaav.
And then there was his cheap shot on Lina to get his hands on Galvayra...a pressure point shot to put her out? Practical.
Lina's fond of this herself. Just watch her first three "fights" in Mipross Island in the first movie.
Most characters in Blade of the Immortal, except the truly bushido believing samurai (and sometimes not even those), are like this. The sympathetic villain Anotsu even based his entire sword school Itto Ryu on this concept, saying that the only thing which matters in a fight is that you win and survive but not how. His main goal at the beginning of the series was even to destroy other schools who, in his view, only teach fancy moves by making their students hit immovable practice targets.
Afro Samurai has no trouble with breaking most of the rules of bushido if they'll save his life. One of his trademark moves is using an enemy as a Human Shield. He'll use innocent bystanders, too.
Jet Black from Cowboy Bebop is something of a master of this trope, utilizing head butts, glass bottles, the element of surprise, and his own spaceship to deadly effect; in one instance he is able to turn the tide of battle against a much better trained opponent by stopping a bullet with his own bionic arm.
Gin's philosophy is to strike like a snake in battle. As a result, he'll use his haori to hide his blade so that he can ambush-strike someone through his clothing. In the anime, he is even willing to throw dust into Hitsugaya's eyes when they fight.
Ganju knows he's not strong enough to defeat Yumichika. He uses every dirty trick in the book hoping that Yumichika will drop his guard because it's so obvious they're not equals in battle. It's his only chance, it allows him to target Yumichika's hair with a firework, and it works.
Iba tries to teach Ikkaku that he should be much more willing to fight to win, not to fight for his ideals. He becomes particularly harsh in his criticism when Ikkaku throws a fight to protect his ideals, pointing out the only people who can afford to be idealistic on the battlefield are those who are strong enough to get away with it.
While putting Ichigo through Training from Hell, Ginjou slashes Ichigo's eyes to blind him. He also invites Orihime onto the battlefield just so he can put her life in danger because he knows Ichigo fights best when someone needs protecting.He also sets up an ambush for Uryuu, using Tsukishima as bait to distract Uryuu while he strikes Uryuu's bow-arm, mangling it beyond use.
Momo Hinamori knows she lacks physical strength, but she has very strong spiritual power which gives her high proficiency in Kidou. She is therefore more than willing to secretly lay a Kidou net around the battlefield to ambush the enemy and then set fire to her trapped foes, knowing that she cannot beat them in an outright brawl.
The Onmitsukidou believes in dirty fighting, teaching that seeing a comrade being killed in front of you is just a good opportunity to stab the opponent from behind. While Soifon preaches these teachings, she is a showy, head-on fighter who explains her philosophy and tries to protect her comrades. Aizen bluntly observes she's mad for dismissing her own organisation's philosophy in favour of fighting him openly and honourably.
Yhwach takes advantage of every opening the enemy gives him. He told the Shinigami war would begin in five days, but attacks in less than 24 hours simply because Ichigo has gone to Hueco Mundo and cannot come to Soul Society's rescue. He tricks Yamamoto into revealing his Bankai too soon, which allows him to defeat Yamamoto's power. He comments that those Stern Ritter who fight less pragmatically than he'd hoped are fighting naïvely, although even the most "naïve" are willing to attack while the Shinigami are introducing themselves or calling their attacks.
Unlike most Blood Knights, the First Kenpachi, Yachiru, does not believe in holding back or fighting honourably. She goes for a killing blow as fast as possible and even draws a dagger with her free hand during a Blade Lock. First Kenpachi Yachiru is better known as Captain Unohana.
And on a larger scale we have Balalaika of Hotel Moscow, who fights her mob wars like military operations. Her men smashed the Washimine Group special forces-style, complete with snipers, frag grenades, flash-bangs, explosives and whatnot and suffered no casualty; the only loss from Hotel Moscow is the ex-KGB and his men, who is not part of Balalaika's ex-airborne troops and who she never likes anyway. She does not fight her enemies, she ruthlessly annihilates them with overwhelming force.
Despite often winding up in unfair fights anyways, most of the cast of Fullmetal Alchemist pull dirty tricks in at least one big fight, if not all of them.
Ed is a good example—in one fight he gets a foe to drop his guard by shouting to his brother Al (who has not just sneaked up behind him), and in another he realizes that the ninja he is fighting gets sloppy whenever her master is insulted and milks it for all it's worth. The first time he "beats" Alphonse while sparring he throws a towel in his brother's face and knocks him to the ground before he can react, while injured heavily enough that Al is afraid to hit back.
Wandering emperor Ling uses this tactic on Envy by throwing sand into his eyes when the homunculus, after snaring him, offers a sadistic choice on how he should kill him. Envy shouts at him in shock and anger on his cheating trick, but Ling counters that all the years of constant assassination attempts on him had made him willing to use any dirty trick in the book to live and run his country.
Major General Armstrong is also a big proponent of pragmatism, although on a more abstract scale. She considers racism a luxury she cannot afford, because she needs varying viewpoints to evaluate the best course of action. She will also pursue any technology or any form of alchemy that will give her troops an advantage in combat. During Sloth's raid into her base, her first reaction is sack him with anti-tank recoilless rifle. When that failed to stop him (and at that point, Sloth is pretty much The Juggernaut), she opts to freeze him using northern cold climate. Practical indeed.
Pretty much everyone in Darker Than Black, but particularly Hei. He attacks from ambush whenever possible, and is particularly fond of electrocuting his enemies through anything handy, be it a pool of blood, a car, or a well-thrown choke wire. If he's in a bad situation, he ninjas away, and at one point even jumped off a building so he could come back a few minutes later and attack his opponent when he wasn't expecting it. His lack of compunctions about cheating is one of several reasons for the Fan Nickname "Chinese Electric Batman."
Villains do it too, though sometimes more in the Kick the Dog territory...
In Medaka Box, the Abnormal Munakata turns out to be a combat pragmatist, though strange; he starts out fighting with multiple swords pulled out of Hammerspace, and once he determines the way Zenkichi fights(barehanded, by the way), he pulls a gigantic mace out of nowhere. When Zenkichi catches it with his shirt, Munakata pulls out pistols.
Though it turns out that it's actually a strange case of heroic bluff: While Munakata does indeed have a pretty big urge to kill, he's also perfectly aware of the consequences of ending someone's life, and how much of a tragedy it is. So he merely pretends to be a dangerous combat pragmatist, by progressively using weapons that are more and more dangerous as the fight advance, hoping that people will simply back up, and not trigger his constant blood lust
You wouldn't expect it from Hellsing, which might be better titled "Blood Knights Come to London" (Call forth your demons, regenerate your legs! FIGHT BACK! and of course Gentlemen, I love war...) but then we recall Bernardotte giving a little speech on how humans fight vampires, complete with demonstrations. And the memorable assertion that claymore mines are just things, they have no killing intent.
Just about everybody in One Piece, but considering it's about pirates it's to be expected.
Most notable on the heroic side is Usopp. His fighting style revolves around playing dead, distracting his enemy with horrible phrases or noises, smoke screens, oil slicks, etc. The first opponent he defeated by playing dead, hiding, dousing him in high proof alcohol, setting him on fire, and pounding him with a hammer until he stopped moving. It was played for laughs. He defeated another opponent by discovering her fear of spiders and attacking her purely at the psychological level. He renders her unconscious, foaming at the mouth, using supplies he scrounged up and never having to deal any physical damage.
For the bad guys, the early villain Don Krieg is the absolute king of this trope. Nothing is beneath him when it comes to claiming victory. One of his standard strategies is raising a marine flag to get in close on other marines, or pretending to surrender just to fire when his opponents put their guard down. He is seen accepting food at a resturant. Promising he will not do anything after getting his strenght back. When this occurs, he figures the resturant will be a perfect disguise, as nobody will expect an attack from it, and decides to take it for himself. When it comes to actual fighting, he relies on an insane ammount of weapons: an extremely though armour with hidden guns all over it, diamond-imbedded gauntlets that lets him shatter just about anything, shuriken launchers in his shoulderplates, lots of bombs, needle machine guns, again in his shoulderplates, poison bombs, a spiked cape, a wrist-mounted flamethrower, an iron net he can fire to pull opponents into the sea, and last but not least, his main weapon: a one-ton spear that explodes whenever he hits something with it. Every time he strikes with it, without breaking.
Two other villainous examples are Diamante and Pica of the Donquixote Pirates; the former even borders on Dirty Coward levels. When fighting Rebecca in the Corrida Colosseum, Diamante steps on her foot to block her and prevent her from moving, before attacking her. Later, when fighting Kyros, not only does he focus almost exclusively on the now-defenseless Rebecca, but he also shoots Kyros's only leg, to prevent him from dodging his Deadly Rain of Spikes of Doom. In the later stages of his fight with Zoro, Pica delberately avoids him to go and try to finish off the other fighters, who were already heavily weakened; much to Zoro's anger.
Luffy himself bites, hits people in the crotch, takes human shields, and has hit more women than Ike Turner. Though he does have some rule such as not ganging up on his opponents, and hitting them in the back.
And when trying to rescue Robin during the Enies Lobby arc, he ends up having to fight Rob Lucci. Throughout the whole ordeal, he's constantly trying to abandon the fight and go after Robin, since she's more important than a fight with the "pigeon guy". He only begins to take the fight seriously once he helps Franky get past, to make sure he defeats Lucci so that he doesn't go after the rest of his crew.
Holyland points out several times the differences between sparring in the tournament or training context and fighting on the tough streets where one has to do whatever it takes to win.
Kyou Kara Ore wa!!!!: being a manga about school delinquents pretty much every character tried something dirty at least once. That said, the protagonist Takashi Mitsuhashi outclassed everyone: when fighting a supposed yakuza and a street gang, he feigned being stabbed to beat the enemy scared by his willingness to fight even when dying, and then convinced his best friend to cancel his debt; when facing a bear (it was actually a man in a suit, but Mitsuhashi didn't know), he suddenly kicked it in the crotch with all his might; when facing a huge American wrestler who could shrug his every punch or kick, Mitsuhashi got him in a chase until he was tired before slugging him; he routinely uses people as weapons and baits, especially if he's supposed to help them. In fact, when he stormed a delinquent-filled school, his allies fully expected him to use them as expendable baits to get at the enemy leader (they were OK with that, as long as he got at the enemy leaders. He slugged him in front of his henchmen). And don't even try martial arts or knives: he's still stronger and faster than any martial artist he faced but one he outsmarted, and when a guy tried throwing knives at him he caught all weapons with a ping-pong racket.
As of chapter 238, Mitsuhashi has been topped by the current foe, Kitagawa: he brought a gun to a fistfight. Partially subverted when he's scared by Mitsuhashi's ally Takasaki and miss him three times at point blank.
In Rebellion, she seems to engage in a fair fight with Mami; but they're evenly matched, so Homura shoots herself in the head to make Mami panic and let her guard down. (Mami didn't really want to kill her, and was unaware that Homura's soul gem allows her to survive a headshot.) It works, but Homura still loses, because Mami was being even more underhanded— she was actually fighting with a ribbon-puppet clone of herself, indistinguishable from the real thing until it suddenly ensnares Homura.
Almost everyone in Claymore have no hesitation to fight four on one, strike without warning or play dirty. The only person who does insist on fighting fair is a young and naive Claymore whose idealistic mindset ends up driving her to become the Big Bad.
Jim: Hey Gene, let's beat this guy.. even if it means fighting dirty. Gene: You got it. The fun's just getting started.
Air Gear:it's easier to count the amount of times the protagonists have bested their opponents without recurring to cheap tricks than an actual straight fight, to give an example, in a battle aboard jets (yes, the kind that fly at supersonic speed, don't ask) Kazu and Agito/Akito team up against two opponents, each team combines their respective strongest attack and charge head-on, but turns out Kazu and Agito/Akito where just an illusion and their opponents fell to the sea because there was nothing to clash on.
Balsa the spearwielder in Moribito: Guardian of the Spirit. When injured and outnumbered she rushed one of her attackers, and smashed him in the head with rock in one swift motion, before collapsing moments later.
Mylene from 009-1 is a very effective Action Girl and has no qualms about using all the tactics she can when she fights. The way she beats Egg is notable. She reveals that her earrings allow her to track and dodge incoming bullets and takes them off. Egg in turn tells her that his eyes allow him to read her next move and agrees to fight their next duel at night. Mylene wins and reveals that she lied — her super-sensitive hearing is built into her body.
We have Eudial, who, in her battles against the Sailor Senshi, discards magic or complicated plans and uses guns that can extract an Heart Crystal faster than the Daimons that she brings with herself only to provide cover for her escape, flamethrowers capable to overpower Sailor Moon's attacks, and even a few dozens machine guns! The latter serve to show why you don't just shoot the Sailor Senshi: the machine guns shoot and hit Sailor Neptune until they ran out of ammo, and, while battered, she isn't even bleeding.
In the manga version, Minako. Some of her greatest hits are: throwing a Precision-Guided Boomerang from behind; Flash Step followed by a kick in the face (with the power apparently increased by the kinetic energy of the Flash Step); and using a cloud of sulphuric acid on an horde of enemies (and as a non-lethal option to boot: it was diluted enough it only stunk horribly). And of course, if it's to protect Usagi, whom she shows Undying Loyalty towards, she'll kick her own fellow Senshi across the room, having no problem with potentially seriously injuring her.
Zoisite in the '90s anime is a mix of this and Dirty Coward. He never fights fair, but he employs a number of tricky methods in order to get the Seven Rainbow Crystals. And it works: He manages to walk away with four on his own, steal one from Sailor Moon and finally nab the other two from Mamoru. He very nearly succeeds, until he makes the mistake of killing Tuxedo Mask. Sailor Moon cries over him, her tear becomes the Silver Crystal and everything falls apart for Zoisite from there.
Nanashi gives a lesson on combat pragmatism during his first fight sequence. He uses his sheathed katana to toss a cooking pot filled with boiling water at the aggressor, and then ends up killing another guy without even having to DRAW HIS SWORD.
He doesn't have a monopoly on the trope though, as pretty much everyone but Luo-Lang qualifies to some degree or another. Luo-Lang is exempt because he's like a foot taller than everyone else, and hops around like Yoda on crack.
This suddenly becomes abundant in Fairy Tail during the X791 arc. Raven Tail resorts to holding a child hostage and getting outside interference in battles to beat Lucy, while Fairy Tail slips Jellal into their team disguised as Mystogan. Mavis allows this because he's one of the strongest mages shown thus far, and she wants Fairy Tail to win.
Habara of Daily Lives of High School Boys, despite being a reformedbully, still has absolutely no understanding of the concept of fair play. She doesn't punch, she gouges. She was even ready to bash her friends Yanagin and Ikushima's heads in with a large piece of rock when they prepared to fight each other. Cue an "Oh Crap!" reaction from both girls.
Lelouch gladly exploits every possible advantage to win his battles, including causing a devastating landslide at one point to bury a sizable portion of the enemy force (and the town below). His idea of a fair duel is to bring in allies and drop the terrain out from under his enemies.
Luciano Bradley also uses these tactics, except he does it because he's a sadist who likes to torture his victims and commit murder on a grand scale, not out of any need to do so.
Zagi Fenrir of Jyu-Oh-Sei. His favorite strategy in a one-on-one fight is to deliberately drop his sword, blind the enemy with his cape, and then kill them with a hidden blade. This is about as honorable as his fighting gets; he also might decide to slaughter an entire Ring of people without warning just because they happen to be in his way. Other characters try to call him out on this, to which he responds with scorn.
Elfen Lied has several examples, because most fights are high risk, they'll do anything to win.
Lucy uses numerous tactics, often throwing nearby objects at her opponents in rapid succession. If an opertunity presents itself that distracts her opponents, she will seize it and move in for the kill.
Bando dips into Crazy-Prepared territory, getting his fight with Lucy in a place where he set up, hid traps, and cleared of debris for her to throw.
The Unknown Man displays himself to be Badass, by taking down two ittle girls and a puppy (he got the drop on the diclonius). When confronted with a man his own size, he opts to beg, all the while reaching for his weapon. He prefers to use that weapon rather than get into a fair fight.
The Agent just witnessed an entire squadron of troops, and some dicloni wiped out by Lucy (several squads). So she just waits at the side for Lucy to start torturing her opponents, before using the remaining half of a cloned Dicolnius to tear off one of Lucy's horns, and then shoot the other off which knocks the girl out, being the only human to ever defeat her.
In Gintama, during a samurai showdown between Kondo and Gintoki, Kondo's wooden sword snaps off at the hilt just as they start charging at each other. Kondo ends up KO'd in one hit. Turns out Gin had glued the blade to the handle, rigging the fight beforehand.
GaoGaiGar: Guy Shishioh may be the world's strongest, bravest and most heroic cyborg, but he's not above sucker-punching his enemy right after it regenerates.
An unusual example is found in Scrapped Princess The main character has a power that severely weakens nearby agents of the Big Bad if she is directly attacked. An ally concludes, correctly, that it doesn't matter who attacks her.
Being a Deconstruction Played for Laughs of the Fighting Series, Muteki Kanban Musume deconstructs this trope with Megumi, whom since childhood realized that she could never beat Miki in a fair fight, so she’s willing to do anything to defeat her that doesn’t involve direct combat, no matter how cowardly or wrong. Even so, Megumi really hates herself for this, so much she believes herself a Card-Carrying Villain to cope with this, and has developed a Guilt Complex so enormous she is convinced that Kayahara Sensei is an avenging ghost decided to puhish her.
New Grappler Baki starts with the appeareance of five supercriminals, who fight some of the main cast. Tokugawa states that theirs will be a confrontation between the shining martial arts and the dark martial arts; the later are the ones who use absolutely everything to win, including weapons and dishonourable tactics. That's on a series that considers Eye Scream and Groin Attack as fair tactics.
Ryuko from Kill la Kill is not above dirty tricks and dishonorable tactics (and running away when she knows she's outmatched.) Perhaps most exemplified with her Naturals Election fight with Jazukure, when Senketsu suddenly develops a flight mode. Since her whole reason for participating is to get information out of Satsuki, who's standing on top of the academy away from the fight, she suddenly tries to abandon the fight to go after her directly before Jazukure intercepts her. Then, after taking out Jazukure's flying machine, attacks her while still in flight mode despite her protests that she should instead go back to normal to fight her as well.
Jazukure herself also displayed some Loophole Abuse during the fight. Since the fighters are only disqualified for falling off the arena, not flying above it, she just flies out of reach and bombards Ryuko with missiles.
Pretty much everyone in City Hunter. As the protagonist is a Hitman with a Heart it's to be expected (and the understanding for duels is: if you exchange guns you give your enemy a loaded gun, and the rest is allowed as long as it's not explicitly forbidden in advance), but seeing the hero whip out tear gas or hide sleeping agents in his trunks it's a bit over the top...
In Tiger Mask we have everyone. Being a manga on wrestling, it's to be expected, because, as pointed by a number of characters (including a Real Life champion and the resident Cape), pulling an illegal move and interrupting it before the referee ends the count is not illegal. In fact, Mil Mascaras' and El Sicodelico (the afore-mentioned cape) complaint with this is not that the world champions aren't too shy to use dirty tricks to win, but that it took them so long to realize they didn't have to not use them they are too set to learn them.
That said, Tiger's Cave wrestlers have so dirty that, for them, dealing with being set on fire is part of the training (for another thing, but it came handy when one of their pupils actually got himself doused with gasoline and his cape set on fire, as he knew exactly what to do to prevent the fire from spreading to him wounds and use the burning cape as weapon) and using pepper to blind their foes is holding back: when they get serious they'll do such things as injecting paralytic poisons on you mid-fight and power-up an headbutt with a cannonball. That said, the protagonist Tiger Mask, being a former Tiger's Cave wrestler and their best pupil in history, is, when pissed, so dirty other Tiger's Cave wrestlers are disgusted and scared, and his whole story is not about him becoming stronger but becoming capable to become a legal Combat Pragmatist: before actually learning this he would force himself to fight fairly, until some opponent would piss him off so much he'd relapse into Tiger's Cave all-out brutality.
Issei Hyoudou in High School D×D fights dirty. He'll try to exploit any weakness in any situation regardless of what enemies do. He'll also have their guard down just in time for him to do something crazy enough to work. The most shining example would be when he took out Riser with two holy bottles, a Powered Armor, and luring him into a trap.
Matic from the Strider manga. The man's unrepentant evil and has no qualms over using underhanded tactics and manipulation to get what he wants, in spite of the fact that, as the Striders' second-in-command, he'd be a certified One-Man Army. This is best demonstrated in the final chapter, when he corners an exhausted Hiryu with two armed mooks, and gloats he's in no shape to avoid the bullets this time. When forced into a one-on-one confrontation with him, however, he finds himself intimidated by Hiryu's determination to win, and so after noticing a large crowd of lesser Striders has gathered (which he believes are all loyal to him), wastes no time in ordering them all to kill Hiryu on the spot.
The two Striders under his charge, Arana and Kubira, are also not above using ambushes or setting up traps to kill him. Kubira actually justifies it as, having been in training school with Hiryu, he's well aware of his monstrous strength and skills and knows very well that, in a direct confrontation, he'd have no chance of victory.
Yusuke Urameshi from YuYu Hakusho, due to his street brawling background. During his battle with Sensui (or his Minoru personality at the time), Yusuke uses his wet T-shirt to wrap Sensui's arm and pull Sensui closer to him. Not only does this restrict Sensui's attacks, but it makes it easier for Yusuke to pummel the living hell out of him.
Sensui: What is this mockery? This isn't martial arts!
Yusuke: No, it's called street fighting. I guess you didn't see it coming!
In Aldnoah.Zero, Inaho Kaizuka has to use every clever trick in the book to defeat his opponents, because they are piloting physics-warping Super Robots, while he is piloting what amounts to a Real RobotMecha Mook. In non-mecha terms, it's like fighting a tank with a slingshot, and Inaho has no choice but to exploit every weaknesses his enemies have with cold and ruthless efficiency.
Qwenther from Heavy Object is this in spades. His default strategy is to use more C4 than an enlisted student has any right to carry into combat. However, when dealing with unstoppable super weapons like Objects, you need to know every trick in the book. His accomplishments include: sabotaging the self-destruct sequence of an Object and then setting it off with C4, exploiting loopholes in an Object's AI control program to make it completely freeze up, using gunshots as Morse code to communicate the enemy's position to an allied Object, using diamonds as improvised shrapnel to destroy a heavily armored mining powered suit, and immobilizing an enemy Object with an IR Jammer. And all that still doesnt compare to the time he defeated one of the most powerful Objects ever seen in the novels by using bed sheets, lemons and milk.
Often done in the Pokémon anime as a strategy against villains such as Team Rocket. While they themselves often play dirty, the heroes aren't against using larger numbers or trickery that doesn't abide by battle rules. As they lampshade at times, why should they fight fair against the bad guys?