Trial by combat
A trial by combat:
- May be requested at any point before or during a trial.
- May be advised against, but even sovereign lords and members of the royal family rarely consider denying such a request outright.
- May be converted into a trial of seven if the accuser (or, presumably, the accused) so demands. Available evidence suggests that this request, too, cannot be denied without severe political consequences. In any case, trials of seven are exceedingly rare, happening perhaps less often than once in a century.
- May be fought by the parties themselves, but it is not unusual for either or both parties to choose champions to fight in their stead.
- Ends when either party yields or is killed; or when the accuser takes back his accusation; or (presumably) when the accused declares himself guilty.
During the Faith Militant uprising, Ser Damon Morrigen of the Warrior's Sons challenged King Maegor to a Trial of seven to which Maegor accepted. Ser Damon and six Warrior Sons against the King and his six champions. It was a trial in which the Kingdom itself was at stake. In the end only King Maegor was left alive, the other thirteen lay dead. 
During the reign of Aegon the Unworthy, Queen Naerys was accused of adultery and treason by the knight Ser Morgil Hastwyck, Prince Aemon the Dragonknight defended his sister's honor in trial by combat and slew Ser Morgil. This event became famous and inspired many songs, stories and fables by bards, furthering Prince Aemon's renown much to King Aegon's annoyance.
The rebellion of Lord Lyonel Baratheon against the Iron Throne during the reign of King Aegon V was eventually settled in a trial by combat between Lord Lyonel and King Aegon's champion, Ser Duncan the Tall who was Lord commander of the Kingsguard. 
Prior to the start of Robert's Rebellion, Lord Rickard Stark, demanded a trial by combat when called to answer for his son Brandon Stark's alleged crimes. King Aerys II Targaryen declared that the Targaryen champion was fire and to prove his innocence, all Rickard had to do was not burn.
A Game of Thrones
When accused by Lady Lysa Arryn of the murder of Lord Jon Arryn and the attempted murder of Bran Stark, Tyrion Lannister requests trial by combat at the Eyrie. Bronn champions for Tyrion Lannister and Ser Vardis Egen, captain of the Arryn guard, champions for Lady Lysa’s. Bronn wins and Tyrion is released.
A Clash of Kings
A Storm of Swords
When Tyrion Lannister is accused in the murder of King Joffrey Baratheon, Prince Oberyn Martell of Dorne offers to be his champion in trial by combat. His opponent, representing the accuser Cersei Lannister, is Ser Gregor Clegane.
A Feast for Crows
The accusations directed towards Margaery Tyrell and Cersei Lannister make both consider demanding trial by combat. Their status as queens makes it necessary for both to choose from the Kingsguard members, at a time when their ranks are seriously depleted. Cersei writes a letter to Ser Jaime Lannister asking him to be her champion.
A Dance with Dragons
|“||The gods know the truth of my innocence. I will have their verdict, not the judgment of men. I demand trial by combat.||”|
|“||The gods have seen fit to proclaim him innocent, child. We have no choice but to free him.||”|
|“||I am innocent, but I will get no justice here. You leave me no choice but to appeal to the gods. I demand trial by battle.||”|
References and Sources
- ↑ 1.0 1.1 1.2 1.3 The Hedge Knight.
- ↑ 2.0 2.1 2.2 A Game of Thrones, Chapter 38, Tyrion.
- ↑ The World of Ice and Fire, Maegor I.
- ↑ A Game of Thrones, Chapter 15, Sansa.
- ↑ The World of Ice and Fire, Aegon IV.
- ↑ The World of Ice and Fire, Aegon V.
- ↑ A Clash of Kings, Chapter 55, Catelyn.
- ↑ 8.0 8.1 A Game of Thrones, Chapter 40, Catelyn.
- ↑ A Game of Thrones, Chapter 67, Sansa.
- ↑ A Clash of Kings, Chapter 2, Sansa.
- ↑ A Clash of Kings, Chapter 20, Tyrion.
- ↑ A Storm of Swords, Chapter 34, Arya.
- ↑ 13.0 13.1 A Storm of Swords, Chapter 70, Tyrion.
- ↑ A Feast for Crows, Chapter 43, Cersei.
- ↑ A Dance with Dragons, Chapter 54, Cersei.
- ↑ A Dance with Dragons, Chapter 65, Cersei.
- ↑ A Dance with Dragons, Epilogue.