Trial by Combat

""I am the Master of Arms. I read up on your combat law. It means I come over here and tell you all the rules, even though everyone here knows them better than I do. Lord Antillus, there, is the challenged. He gets to choose how the duel will be fought. He's chosen steel and fury, which basically means anything goes, which is how fighting ought to be done in any case. Isana is the challenger, which means she gets to choose the time and place of the duel. She has chosen here and now. Obviously. Or none of us would be standing out here in the wind.""

- Doroga, Princeps' Fury

Traditionally, this is one of the three basic ways of resolving a conflict or disagreement between two individuals or legal entities, the other two being Trial By Ordeal, and Trial by Arbitration, for which we have plenty of coverage already.

The idea behind Trial by Combat is very simple, which is probably why it's been used by numerous cultures throughout history: someone is accused of a crime, or two parties are descending into conflict over a matter of opinion or policy. In order to resolve this issue with the minimum of bloodshed, an individual is chosen to represent each side, and they fight. Winner takes all.

This works, supposedly, because Right Makes Might. Whichever side is in the right will win a fight, either because Good Hurts Evil, or because of some kind of divine intervention. Naturally, this idea is passé now, and so the Trial by Combat has become something of a Dead Horse Trope.

Note that there is no need for either the accused or the accuser to fight for themselves. Just as often, they will choose a champion to fight on their behalf, which is good, because otherwise bullies could handily go around accusing pipsqueaks of crimes against them and beating them up for the recompense.

Note also that these fights don't necessarily have to end in death, though they often do, especially if the accused is suspected of a capital crime.

If the trial takes place between representatives of opposing armies, you have a case of Combat by Champion. And of course, if the two are fighting over an insult, it's going to be a Duel to the Death, with all of the Throwing Down the Gauntlet etc. Be aware of the difference between these Duel to the Death and Trial by Combat. Although they are similar and in many cases overlap, Trial by Combat is always sanctioned by the pervading culture whereas a duel is sometimes illicit. Also, the way of engaging a trial is different. While a duel can be arranged entirely between the conflicting parties, a trial must be instigated at the behest of some authority figure (who will preside over the fight like a referee and may themselves serve as champion, especially if they're of a Proud Warrior Race), and there have to be witnesses to verify how things went down.

Anime and Manga

 * In Gundam Wing, Zechs Merquise is court martialed by OZ for disobeying orders and rebuilding the Wing Gundam. The sentence is death, but his friend Treize manages to propose Trial by Combat as an alternate sentence. Zechs is pitted against countless Alliance soldiers, all fighting to win OZ's favor; if Zechs wins he's allowed to go free. Since this is only about one-fifth of the way through the series, of course he wins.

Fanfic

 * In The Basalt City Chronicles, the Empire of Smilodons has a hand-to-hand version of this as a civil, rather than criminal, trial. Only in extreme cases are the fights declared to be to the death, and almost always as a means of getting powerful nobles (who would be otherwise forced into a death match) to stop the feuds between their factions (if you win, your faction wins, but you yourself are exiled).

Film

 * In the film Excalibur, and some of the source materials it's based on, Queen Guenevere is accused of adultery against king Arthur with Lancelot. All of the knights had been afraid to level this accusation because her champion was Lancelot himself, whom no other knight can defeat.
 * In The Canterville Ghost (the 1944 movie anyway) Sir Simon de Canterville runs away from a trial by combat fight (with Tor Johnson), becoming the eponymous ghost after his father walls up the door to his room to prove he isn't there.
 * Occurs (unsurprisingly) in the 1964 film version of Prince Valiant.
 * Also occurs in the 1961 film El Cid.
 * Flash Gordon (1980). When Voltan decides to turn Prince Barin over to Ming, Barin demands a trial by combat under Article 17 of Ming's law. Instead of choosing to fight Voltan, Barin chooses Flash as his opponent.

Literature

 * In Jim Butcher's Codex Alera series, there are at least two forms of this: the Marat have a different form of trial for each clan; the Gargant clan go by this method, calling it "Trial By Strength." Then there's the practice of juris macto among the Aleran people, which is a ritualized and legally binding form of Duel to the Death and covered on that page. Headman Doroga has a few things to say about the "ritual" part.
 * By the same author, in The Dresden Files novel Changes, the Harry and Susan are forced to fight one of these when they are pursued into  by vampires, and   doesn't know who is right. Besides, he likes a good show.
 * Jim Butcher really likes this trope. It also appears at the end of White Night when Harry and Ramirez challenge Vitto Malvora and Madrigal Raith to a duel. The challenge and duel are a long series of Crowning Moment of Awesome, with a priceless Crowning Moment of Funny with heavy applications of sarcasm from the White King of all people when Madrigal and Lady Cesarina Malvora try to duck the challenge.
 * Harry later takes on Duchess Arianna, a severely badass vampire (one level down from and  the Lords of the Outer Night, Physical Gods to a being. However by now Harry has taken several levels in Badass wields Soulfire gifted by the Archangel Uriel and is  . At the end Harry turns Arianna into a crater on the floor.
 * The climax of Ivanhoe culminates in trial-by-combat. Sir Wilfred of Ivanhoe fights on behalf of Rebecca, the daughter of Isaac of York, who has been accused of witchcraft solely on the basis of her being Jewish. Wilfred's victory is seen as a sign from God that Rebecca is innocent. Of course, in the end she and her father are still exiled for the "crime" of being Jewish.
 * Repeatedly used in A Song of Ice and Fire: to wit, Bronn against Ser Vardis over Tyrion's supposed murder of Jon Arynn; Oberyn Martell against Gregor Clegane over ; and supposed to figure into Cersei's plan
 * Occurs in The Knights of the Cross when Danuska gets kidnapped by The Teutonic Knights, Jurand knows the exact culprits but will not implicate them because she is being held hostage. When the order's emissary arrives, he feels insulted that anyone would accuse the knigts when the victim's father doesn't and challenges anyone who would "slander" his brothers in arms to a Duel to the Death . Obviously, Zbyszko takes the challenge.
 * Occurs in the Chanson de Roland (the Song of Roland), when Thierry fights Pinabel to prove the guilt of Ganelon.
 * Chessmen of Mars: Captives in the city of Manator must play a life-sized version of Jetan, with each taking of a piece being a duel to the death. Captives, criminals and slaves can win their freedom by winning enough games.
 * The Whitecloaks in The Wheel of Time use this as a way of settling disputes when there is no evidence, though it has fallen out of practice by the time of the books. However, the lawful-minded Galad uses the tradition to challenge the Commander for the suspected murder of his mother, killing him and winning command of the order as a side-bonus.
 * Honor Harrington engages in 3 duels in the eponymous series. The first two were Curb Stomp Battles, in which she only got wounded because her Dirty Coward of an opponent cheated. The third was specifically this trope, against the traitorous Steadholder Burdette. He didn't even get a chance to make a move before she took his head off.
 * Used in one Brother Cadfael story to get rid of a murderer (and rival in love) against whom there was no real evidence.
 * Such a system is in place in the King Arthur legendarium. Every knight knows that Guinevere is cheating on Arthur with Lancelot, but an accusation without any proof can only be made by challenging the queen's champion- Lancelot himself. Since he's an invincible knight, no one dares asperse her loyalty out loud.
 * Being based on King Arthur and other medieval literature, the country of Arendia in the Belgariad uses this system as well. It comes up in the second book when, because Garion is unable to prove that an ambassador is plotting to kill the king in order to foment war, the renowned and eminently honourable Mandorallan challenges the ambassador in order to prove his misdoings.

Live Action TV

 * In Star Trek: The Original Series episode "The Omega Glory," Kirk fights Captain Tracey to prove to the Yangs that he (and not Tracey) is trying to help them (the Yangs believe that Good is stronger than Evil).
 * In "Arena", he had to face an alien captain in order to determine who was in the wrong over straying into the other's space.
 * In the V (1980's) episode "Trial By Combat", Diana and Lydia fight one to decide whether Lydia is guilty of killing Charles.

Opera

 * Lohengrin fights a judicial combat for Elsa of Brabant in his eponymous opera by Richard Wagner.

Tabletop Games

 * The Clans of BattleTech base their entire culture around this. The higherups made an edict your clan doesn't like? Then the result will most likely be a Trial of Refusal. There are Trials for all kinds of stuff, from the mundane Trial of Bloodright through the politically-motivated Trial of Absorption to the more radical Trial of Annihilation.
 * Trial by combat is still practiced in certain rural areas of the empire in Warhammer Fantasy. Warhammer Fantasy Roleplay even has a class, the Judicial Champion, who represents the local courts.

Video Games

 * In Twilight Princess, Gorons won't let you into their mine until you defeat their leader in a sumo match.
 * In ~Assassin's Creed~, King Richard declares Trial by Boss Battle when Altaïr accuses Robert de Sable of leading a massive conspiracy. At the end, Richard believes that God wanted Altaïr to win, and he must have been telling the truth; Altaïr takes the skeptical approach and tries to convince the king that he was just the superior fighter.
 * In Neverwinter Nights 2, you have to sit through a mostly pointless trial by judge. Pointless because whichever way the judge rules, the losing party will invoke the right of Trial by Combat to give you a Boss Battle.
 * Of course, there are advantages to winning (you're legally exonerated for the crime for which you were framed), and losing (you basically admit that you did it). People react appropriately.
 * This is how the Landsmeet is ultimately resolved in Dragon Age: Origins. Regardless of how well you've curried favor with the nobility, you will still need to fight in a duel to decide who will lead Ferelden against the Blight. Any one of your companions can fight in your stead if you don't want to do it, though choosing Alistair.

Real Life

 * This was used during the Medieval Era as a way to determine "God's Judgement", because (the thinking went) the winner would obviously have been chosen by God to win. Generally, it was easier than the one where you got thrown in the river to see if God wants you to survive.
 * In The Last Duel by Eric Jager, the author describes the last legally sanctioned (Duels to the Death of course continued to the eighteenth century and beyond, but they were more an aristocratic version of a Bar Brawl done with lethal weapons, then a legal practice) judicial duel in France during the hundred years war. A French noblewoman who was pregnant out of wedlock claimed that it was rape by her husband's enemy and her husband, believing her, stood in the lists as plaintiff. The accused stood as defendant. In something of a Zig Zag no one really believed it was an ideal means, the Church condemned it as Tempting Fate and there hadn't been a Trial by Combat in ages. It was only permitted by the French king because the law was still technically on the books because no one had bothered to take it off. And because there was no way to solve a rape case there being no DNA testing at the time. In other words it was permitted not because it was actually believed that God would automatically intervene for the right party but because no one could think of anything better to do and it was technically legal. In any case, as the title of the book indicates it was the last Trial by Combat in France.
 * Notch, creator of Minecraft, challenged Bethesda to a 3 vs 3 game of Quake III Arena to settle a legal dispute. Sadly, Bethesda chose to ignore this challenge.