The 100: No one on this show fights fair if they can help it, but special mention goes to Clarke's fight with Anya. Over the course of the fight, Clarke throws ashes into Anya's eyes, pulls a knife on her unarmed opponent, and finally gains the upper hand by digging her fingers into an open wound that Anya had gotten earlier.
Even when two characters fight a formalized Duel to the Death, punching out one of the guards overseeing the match and stealing their weapon is considered perfectly acceptable.
24: Jack Bauer especially but also many of his opponents. He'll use sneak attacks and break bones, kick in kneecaps, and shoot to incapacitate or coerce. His fighting style is brutal with little or no flourish. This gets taken to utterly pants-shitting levels at times. Early in Day 6 whilst tied to a chair and being tortured, he waits until the mook has his back turned, and removes the cuff on his EKG from his arm, causing it to flatline. He plays dead while the mook comes over to check on him and then takes a chomp out of his neck.
Agent Carter: Lead character Agent Peggy Carter has no problem bashing an opponent with the nearest heavy object until they stay down and takes ruthless advantage of her opponents' preconceived notions of the feminine to get what she needs. Her roommate also shows shades of combat pragmatism if you count mental warfare as she is more than willing to burst into tears and play on Agent Thompson's chivalry and love for his grandmother in order to give Peggy time to escape.
One of the Nietzschean's hats, Nietzschean crewmembers Tyr Anasazi and later Telemachus Rhade are usually the first ones to suggest retreating and/or selling out their allies when a situation appears hopeless. It might seem odd considering their Proud Warrior Race status but meshes quite well with their Social Darwinism, especially considering that their definition of "fittest" is "lives longest and sires the most children".
Being a Combat Pragmatist could have saved the Old Commonwealth, and Dylan's Number Two Gaheris Rhade (a Nietzschean and Telemachus's ancestor) suggests destroying the entire Nietzschean armada by blowing up the system's star. Dylan refuses to destroy an inhabited system, and this proves to Gaheris that the Commonwealth doesn't deserve to survive. Dylan learns a few dirty tricks since then.
Had a few of these, which is surprising considering that it's high fantasy, and the protagonist is nearly indestructible. Especially when considering how over the top its parent show could be. Probably the best example would be Lindsey's hand. Lindsey dangles a scroll that Angel desperately needs to save Cordelia over an open fire while goading Angel. So Angel cuts the guy's hand off at the wrist then casually walks over and picks the scroll up.
And, lets not forget Russell Winters:
Lindsey: "So you kicked him out a window."
The Avengers: A producer's write-up on John Steed, to guide writers of episodes, specifically stated that "he fights like a cad and uses every dirty trick in the book..."
John Sheridan used a distress signal to lure a Minbari capital ship in an asteroid field mined with fusion bombs. Garibaldi put it best:
Garibaldi: "[...] Right now, according to his file, Sheridan is a good tactical thinker. He can take an inferior defensive force and turn it into an offensive force capable of taking on a better-equipped enemy. Now, he did it with the Black Star, he did it during the Mars riots. Now, you ask me, he is the one chance we've got to make it through this thing alive."
A double example with the Black Star: the distress signal was genuine, the ship had been crippled by a Minbari ambush and left for dead, the Minbari were coming to kill a helpless opponent and he took advantage.
What constitutes dirty tricks differs between cultures. The Minbari consider what Sheridan did cowardly, while EarthForce praised him as a cunning hero. Meanwhile, the Minbari fight a war of extermination, killing civilians and not taking prisoners, and consider it honorable.
The Centauri, however, have topped everyone during their war against the Narn. Their reaction to the Narn launching a sizeable part of their homeworld defensive fleet against their main supply base to try and slow down their advance? Have that base guarded by the Shadows while they advance of the Narn homeworld and bomb it with mass drivers (a war crime, by the way).
Batman: If you take out the wacky sound effect frames and just look at how Batman fights in the 60s TV show, you'll see that he gets fairly brutal. At one point, he rips a lead pipe off a wall and beats a mook with it.
Starbuck, particularly during the episode "Scar", wherein Viper pilots are confronted with a deadly, newly-motivated enemy sortie, who utilises all sorts of tricks and decoys.
Starbuck: 'This isn't dueling pistols at dawn, this is war. You never wanna fight fair. You wanna sneak up behind your enemy, and club 'em over the head. You see, Scar understands that. And so do I. So, that's why I'm gonna kill him.'
Of course, the most pragmatic thing Starbuck ends up doing in that fight is swallowing her pride and luring Scar into an ambush so that someone else can take the kill and get the glory.
Colonel Tigh took this trope to a much wider field during the occupation of New Caprica. Suicide bombers, random violence — "I'm on the side of the demons."
Sherlock: John and Sherlock could qualify, but there HAVE been moments when they needed backup from the other. John (surprisingly) was pragmatic with snarky comments, and while tied to a chair at the time, killed a Chinese gangster trying to kill both Sarah and Sherlock. Oh, and he was pragmatic WITH a death threat on a professional killer that had Sherlock in a headlock in an attempt to strangle him, or, worse yet, SNAP HIS NECK! Bad idea. It would've ended, well....badly for the guy. It obviously didn't end well for the Chinese gangster, and it ended BADLY for the cabbie.
The Judge was an immortal demon (meaning that you could cut him to pieces and he'd return alive as soon as the pieces are reassembled) and invulnerable to forged weapon: Buffy followed Xander's advice and shot him with a rocket launcher.
Glory was a goddess too powerful for Buffy to match in normal combat: Buffy and the gang slugged her with the hammer of a troll god and a wrecking ball, and when Glory retreated and left control of the body to Ben, Giles calmly walked up and smothered him, killing a goddess in the process.
Another example of this trope in Buffy is when she kicked Angelus in the groin.
In an early episode, Buffy was at the receiving end of this when a vampire pulled guns on her (Buffy only survived because Angel staked said vampire In the Back.
Burn Notice: Michael Westen. As he explains in the Season 3 episode, "Friends and Family", "Spies are not trained to fight fair. Spies are trained to win." He always explains via voice-over what he's doing and why he's doing it. For example, in a car chase, he explains that small-caliber weapons can't penetrate the engine block, so it's best to aim for the windshield, or try to ricochet bullets up from the ground, as it's really hard to drive when you've got bullets coming at you from under your car.
He once used a copy of Cat Fancy magazine to beat up some loan shark thugs. In the first episode, he teaches self-protection techniques to a kid with a bully problem, including feigning submission and headbutting
The other two members of Michael's Power Trio, Sam and Fiona, fit this as well. One episode has Fiona showing that she had no qualms about subduing a thug she was trying to capture with a well-placed beanbag shotgun round to the thug's groin.
In the very first episode Michael explains that punching people is a great way to damage your hands and that it's better to use the hard surfaces around you instead. He then slams a mook's head into a nearby urinal.
Camelot: Gawain explains the philosophy of pragmatic combat to Arthur and his merry men. It takes them a while to accept the idea.
Community: Pierce in the episode Comparative Religion claims to be using this to try and help teach Jeff fighting, but actually he just wanted an excuse to kick Jeff (and Troy) in the shin.
Deadliest Warrior: Frequently argued about by supporters of warriors who prefer ambush or avoidance tactics rather than the toe-to-toe duels that the show always assumes.
In Deadwood this trope is omnipresent, resulting in very short confrontations, the majority involving guns. One of the most violent characters hangs a lampshade on the avoidance of a fair fight, just after one had happened - and even that was an extremely messy affair where the guy who was going for torture over the quick kill lost, despite having the advantage.
Doctor Who: the Doctor usually shys away from guns. Not so for the Sixth Doctor, who upon faced with an army of Cybermen simply picks up a blaster and dispatches the lot.
In Farscape, Chiana is mostly a cheerful, kooky Ms. Fanservice. Until she's genuinely pissed off and afraid for her life, in which case watch her set people alight or spray acid over them!
Firefly: Most fights include dirty tactics, such has hitting people from behind, throwing sand in their eyes, hitting genitals, surprise attacks, etc.
Captain Malcolm Reynolds, especially, seeing that he has no problem hitting people from behind, turning a duel with swords into a fistfight, shooting horses that his enemies are using as cover, and even throwing people into jet turbines or, worse yet, space.
The Flash (2014): Captain Cold took advantage of The Flash's drive to save people by derailing a train. After Flash saved everybody and stopped to catch his breath, Cold knocked him out from behind.
Game of Thrones: Since this is a series where things don't go well for those who place Honor Before Reason, there are many examples of characters winning this way. Though the series on the whole emphasizes this far moreso than the books which still insists on the superiority of classic swordsmanship, castle training and military service over undisciplined back-alley sneak attacks.
When Bronn wins his fight as Tyrion Lannister's champion by tiring out his opponent with hit and run tactics instead of straight up dueling him, Lysa Arryn reproaches him: "You do not fight with honor." Bronn indicates his slain adversary and answers: "No. He did." When Bronn is called to retrain Jamie Lannister so he can learn how to fight while missing a hand, Bronn tries to teach him how to fight pragmatically, like attacking an opponent who isn't ready, but Jaime finds it in poor taste.
When Daario Naharis is challenged to a duel by a man on horseback, instead of jousting him with a horse of his own, he simply throws a dagger to kill the horse, then kills the man while he's lying stunned on the ground.
Karl Tanner spits in Jon Snow's face to blind him, kicks him in the shin during a Blade Lock, and uses the environment to his advantage. He only loses when he forgets to be pragmatic and turns his back on Jon to attack a woman who stabbed him in the back. Jon learned from this and uses similar tactics to defeat Styr.
A flashback to the Tower of Joy shows how Ned Stark beat the legendary Arthur "Sword of the Morning" Dayne- he didn't. Arthur slaughtered Ned's comrades and, in a one on one fight, dominated Ned and knocked his sword out of his hand, but, before he could deliver the killing blow, Howland Reed ran up and knifed Dayne in the throat from behind.
Loras Tyrell unhorses Gregor Clegane in the Tourney of the Hand by riding a mare in heat against Gregor's ill-tempered stallion. Characters disagree on whether this is cheating.
Jaime pulls a dagger and stabs his opponent in the eye with his off hand when their swords become locked in "The Wolf and the Lion".
Yoren forces a gold cloak to surrender by holding a dagger to his femoral artery, stating that men are so worried about their throats that they forget everywhere else.
Brienne wins a tourney despite being disarmed by tackling her opponent and drawing a dagger.
Lord Tywin scolds Jaime for sparing Ned in the name of a clean fight and asks Tyrion why killing 10,000 men in battle is more noble than murdering a dozen.
Oberyn demonstrates that dagger beats sword in a Quick Draw in "Two Swords". Later, he uses light armour, Hit-and-Run Tactics, and taunting against a larger and stronger opponent.
In "The Mountain and the Viper", Arya declares that anyone who shuns a method of killing as dishonorable will never be a great killer.
Obara Sand allows Nymeria to imply that Obara will stand aside while she and Trystane Martell fight a duel, then stabs Nymeria's opponent from behind without a fight.
Hawaii Five-0: Somewhat Played for Laughs in the episode "Kekoa". Steve tells the Killer of the Week, a trained martial artist, to pick on someone his own size. The killer charges and Steve draws his gun and kneecaps him with an almost bored look on his face.
Highlander: Methos. If the fight's going against him, Methos is not above feigning helplessness (such as pretending to slip) and then, when his opponent moves in for the kill, drawing a hidden dagger and stabbing him.
Methos is the oldest Immortal. He's so old that he doesn't remember how old he is. He remembers the first civilization, and he was already old then. There's only one way to become the oldest Immortal: Be very good to your friends, have no mercy for your enemies, and always, always, know which is which. This was explicitly referenced a few times; many of his friends hail from eras of formal combat and take Honor Before Reasonvery seriously, but he was ancient before honor was even invented.
Recurring villain Xavier hires gunmen to shoot his opponent before he delivers the coup de grace in his second appearance. This goes against the Highlander Code, but he's a villain.
iCarly: Sam will cheat as much as possible in any combat related event. She ran around with an extra half-dozen blowtubes for her game of paintball assassin with Spencer. Apparently she's also knocked out a trucker with a jug of milk, according to Carly.
Kamen Rider Dragon Knight: Grant Stanley- AKA Kamen Rider Camo- is an underground martial artist who is not above attaching wrenches to his fists to win a fight. Karma hits him hard when he is vented (killed, but not really) by Kamen Rider Torque and his massive arsenal of guns.
Kamen Rider Torque is the only Rider with an arsenal of guns; he never fights without using them and it is rarely a fair fight. He is only defeated by Kamen Rider Strike- whose vicious and close-range fighting style and powerful contract beast (and pension for dodging bullets) rendered Torque's guns useless. It is demonstrated quite clearly that Torque cannot fight at all without his weapons.
Many of the Riders have tactics and weapons that could be considered dirty, even the heroes: Siren can transform into a storm of feathers and Wing Knight can spawn clones of himself.
Kamen Rider Ryuki is a series about 13 Riders fighting a battle to the death. Some of these Riders are combat pragmatists. Most notable are Shuuichi Kitaoka/Kamen Rider Zolda, who prefers to just shoot other Riders with his arsenal of ranged weapons when his target is unaware and Takeshi Asakura/Kamen Rider Ouja, who is savvy enough to attack The Hero during his Transformation Sequence, crippling the guy, thus giving him an unfair advantage during their fight.
Law & Order: Special Victims Unit: In the Season 10 episode, "Crush", Stabler attempts to question an arrogant suspect in a gym in a boxing ring, only for the guy to tell Stabler to wait until he's done. Stabler gets into the ring, and the guy to takes a swing at him. Stabler dodges it and knees him in the balls, to which the suspect yells that it was a cheap shot, to which Stabler replies, "I though it was a street fight".
Legend of the Seeker: In one episode, Kahlan is kidnapped and kept in a dungeon. She finally escapes after the guards give her a plate of stale bread to eat. She takes the metal plate, folds it in half, creating a sharp corner, and stabs her guards with it. Stay in the Kitchen does not work on this woman.
Reese: So, once you've taken out his eyes, you can take your time and really get creative. Personally, I like to leave at least one sense working, so he can tell what's happening to him.
Married... with Children: In one pirate-themed episode, Captain Courage (Al) and Rubio the Cruel (Steve) are sword fighting for Scarlett's (Peg) freedom, Rubio boasts, "How can you think to beat me? I was taught swordfighting by the finest teachers of the finest schools in Europe!" Courage simply says: "Oh yeah, I learned in the streets!" and knees Rubio in the nads, winning the battle. Bud also applies this trope on a few occasions. When he gets into his first barfight at the nudie bar, a seasoned veteran decides to give the "rookie" a free shot. Bud immediately smashes him over the head with a chair, which makes Al very proud.
Merlin: Merlin is enough of a Magic Knight to give lower enemies a fair fight with a sword...but why would he do that when he could just use his magic to hit you with your own weapon, trip you up, drop tree branches on you, or disarm you and let his Master Swordsman best friend King Arthur clobber you? He even cheats for Arthur in a few occasions, breaking the saddle girth on mounted knights and disarming Arthur's opponents even if it looks like Arthur could handle them, just in case.
Dr. Julia Ogden is a prime example of a Combat Pragmatist. She will attack you from behind or use her skill with scapels to mortally injure you (see "Snakes and Ladders") if you attack her or someone she cares about.
Dr. Emily Grace takes after her mentor. In "Murdoch of the Living Dead", when she was grabbed by one of the "zombies", she stabbed him in the hand with her hatpin , and in "Friday the 13th 1901" she hit Julia's ax-wielding attacker from behind with a bottle.
Anna Fulford in "The Murdoch Identity" is quite handy with a frying pan, and later in the same episode she shoots one of Murdoch's captors and pistol whips one in the back of the head.
In "Victoria Cross", Murdoch himself comes upon a killer approaching Julia and her patient (an eyewitness to his earlier robbery and murder), and grabs the guy's arm from behind without further ado—no flashing the badge or issuing a verbal order to stop.
The Office (US): The duel between Michael and Dwight proves the point. While Dwight uses honorable combat and martial arts, he gets easily defeated by Michael's schoolyard bully tactics. Plus there was that other duel Dwight fought against Andy. Dwight again tried to fight honorably, but Andy opted to use his electric (and therefore silent) car to sneak up on Dwight and pin him against a fence.
While in professional wrestling cheating to win a match usually makes you a bad guy, several noted wrestlers have gotten famous as nontraditional babyfaces who beat the heels through all manner of dirty tricks. The two most famous examples would probably be Eddie Guerrero, who would win matches by (among other things) throwing a chair to an opponent behind the referee's back and flopping to the mat as though he had been hit (thus getting them disqualified) and was one of the most beloved men in the industry despite having "I lie, I cheat, I steal" as his personal slogan, and the legendary Ric Flair, world renowned as "The Dirtiest Player in the Game" who would beat the opposition with eye gouges and the dreaded "testicular claw".
Finlay, in his current WWE run, is a more recent example. To Finlay, every part of the ring is a weapon, including the apron (which he utilizes as a net to trap wrestlers trying daring-leap-to-the-outside or baseball-slide maneuvers). And, just in case things start really going south and he needs a real weapon, he always has his shillelagh waiting for him in the corner. And did we mention he's a Face?
And then there's Money in the Bank, a Gimmick Match whose winner can claim a title shot any time within the next year. It usually gets cashed in right after the current champ has gotten thoroughly beat up by someone else.
Revolution: Miles prefers to just kill his enemies, so they don't bother him later. "Chained Heat" has him sparing the bounty hunter Jacob at Charlie's urging, but when Jacob sells them out to the Monroe militia, Miles makes sure to kill him off the second time they meet. "Nobody's Fault But Mine" has Rachel lulling the psychopath rapist Will Strausser into a false sense of security before stabbing him in the heart.
The Rockford Files: Jim Rockford definitely fits. Whether it's low blows, improvised weapons, or distractions, he uses any dirty fighting technique he can think of. Lampshaded in one case, where he makes sure he has the Mook's attention, goes into the bathroom, spreads soap all over the floor, slips a roll of quarters into his hand to up the impact on his punch, and, when the guy follows him in, goads him into attacking first so he'll slip and be easier to cold-cock. He then tells the recumbent idiot that "the problem with Karate is it's based on the ludicrous notion that the other guy is gonna fight fair."
Seinfeld: One episode has Jerry and George ask Elaine which of the two would win in a fight. Elaine says George, on the basis that he would fight dirty. George happily admits it, and Jerry happily accepts it. This is confirmed in a later episode where the three of them fight, and George does win.
The Shannara Chronicles has Eretria, a wandering thief who doesn't believe in fair fights. When challenged to fight like gentlemen by Amberle, she dismounts her horse, walks up to her...and headbutts her as she's asking for a sword.
Wil: That was hardly a fair fight! Eretria: Life isn't fair.
Smallville: Clark Kent of all people does not believe in a fair fight. His usual strategy boils down to "clock you in the head from behind at 500 miles an hour." Tess Mercer is just as bad, if not worse.
Stargate SG-1: In general the SGC is an entire command of combat pragmatists due to being in the sights of a civilization that does nothing but conquer and enslave. Lampshaded in the episode "The Warrior".
O'Neill: (Holds up a staff weapon) This is a weapon of terror. It's made to intimidate the enemy. (Holds up a P90) This is a weapon of war. It's made to kill your enemy.
Stargate Atlantis: In one early episode, Teyla hands Sheppard's ass to him in a sparring match with melee weapons, and Teyla remarks that if it were a real fight, he'd be dead by now. Sheppard replies that if it were a real fight, he would have shot her by now. You don't bring a couple of sticks to a gun fight.
For reference, while Teyla frequently practices hand-to-hand fighting, she always goes to missions with a submachinegun.
Any Runner (like Ronon) is, by necessity, a Combat Pragmatist. Either they use any means to survive and kill their pursuers, or they die.
Weyoun. More about strategy than actual throw-downs, the idea that there are 'rules' in combat is a notion he is only aware of so that he can manipulate other people. This may be a trait of the Vorta in general, given that they are a genetically engineered race.
Major Kira. As has been noted elsewhere, fair tactics do not keep one alive in the Bajoran Rebellion. Therefore, Kira doesn't use them. Deep Space Nine didn't shy away from calling the Bajoran Resistance fighters terrorists. Terrorism is generally referred to as perfectly legitimate tactics, and not just in the back story. Of course, they are defending their own planet so the only people they were terrorising were the invading Cardassians, and the word 'insurgency' hadn't come into vogue by then.
By Klingon standards General Martok can seem like this. He is perfectly willing to perform hit and run, and strike weak enemies, and cut-off supply lines rather than directly engage. Being a Klingon, he really doesn't like these tactics (they're not very fun), but he feels that winning the war is more important than earning honor and glory in individual battles.
Klingons as a whole are this. During the invasion of Cardassia, the Klingons hide cloaked ships in debris fields following battles to ambush any potential rescue ships. When Dr. Bashir says this doesn't seem like an honorable tactic, Worf merely says 'In war there is no greater honor than victory'.
Species 8472. Federation forces repeatedly try to fight the Borg conventionally, ship-to-ship, and each time get their heads handed back to them on a nice platter. 8472 blasts Borg planets apart, not only eliminating large quantities of Borg forces at once, but also denying supporting infrastructure permanently.
In another episode, where the Doctor had been left in command of the ship, an alien ship called to inform him that they were going to seize Voyager as a derelict vessel (the crew had been driven off by a radioactive mine). The Doctor responded by immediately firing on the alien ship and crippling it.
Terminator: The Sarah Connor Chronicles: Cameron does not know of any other way to fight. For example, at one point she casually shoves another Terminator through a wall and blows its prone body apart with a grenade launcher. She also has no qualms with dropping a Terminator down an elevator shaft, and then dropping the elevator on said Terminator. Being a Terminator herself and given the kind of opponents she faces, this pretty much comes with the territory.
The West Wing: Campaign consultants Bruno Giannelli and Lou are political equivalents of this, in contrast to most of the other protagonists, who are more principled and idealistic.