Trial of seven
The trial of seven is a form of trial by combat an offended party can demand during trial. It is linked to the Faith of the Seven and Andal tradition. The Andals believed that if seven champions fought on each side, the gods thus honored would be more likely to see justice done.
The accused is declared innocent if his accuser or accusers are either defeated or yield, thereby withdrawing their accusations. If the accused is slain, it is believed the gods have judged him guilty, and the trial of seven ends. If the accused cannot find six men to stand with him, he is declared guilty as well.
The trial of seven came to Westeros along with the Andals. In 42 AC during the Faith Militant uprising, Ser Damon Morrigen of the Warrior's Sons challenged King Maegor I Targaryen to a trial of seven, believing the right to rule the Seven Kingdoms did not belong to Maegor. Maegor accepted the challenge, and faced Ser Damon and six other Warrior Sons with his own six champions. While the tales about the trial are often contradictory, they all agree that Maegor was the last one standing. However, Maegor was severily injured by the last of the Warrior's Sons, and fell to the ground himself shortly after killing his last opponent.
The next trial of seven in Westeros occurred during the Ashford Tourney in 209 AC. After a hedge knight named Duncan attacked Prince Aerion Targaryen in defense of a dornish puppeteer, he was challenged to a trial by seven by both Aerion and his older brother, Prince Daeron Targaryen, who had falsely accused Duncan of having kidnapped Prince Aegon Targaryen. The princes Aerion and Daeron were aided by their father, Prince Maekar Targaryen, three knights of the Kingsguard, Ser Roland Crakehall, Ser Donnel of Duskendale, and Ser Willem Wylde, and Ser Steffon Fossoway. On Duncan's side fought Prince Baelor Targaryen, Ser Lyonel Baratheon, Ser Robyn Rhysling, Ser Humfrey Hardyng, Ser Humfrey Beesbury, and Ser Raymun Fossoway. After Daeron was defeated and Aerion withdrew his accusation during the trial, Duncan was declared innocent. However, Prince Baelor had been severily injured during the trial, and died shortly after. Humfrey Hardyng and Humfrey Beesbury died as a result of the trial as well.