A trial by combat is a means by which a party can prove their innocence when accused of a crime in the Seven Kingdoms. In lieu of a standard trial where a lord hears testimony from the involved parties and makes a ruling, one or all parties may choose the option of a trial by combat.
In a trial by combat the accused may represent themselves in combat or, if unable (such as if they are female, injured, crippled, a dwarf, or otherwise incapacitated), may ask for a champion to represent them. The victorious party is held to have had his or her case judged fairly by the Seven (or other faiths such as the Red God) and has proven their innocence in the eyes of the gods. Hence, they are cleared of all charges.
Refusing to have his fate judged by the obviously partial and under-aged Lord Robin Arryn, Tyrion Lannister demands a trial by combat. As Robin is underaged and his mother Lysa Arryn cannot fight, Lysa names Ser Vardis Egen, the captain of her guards, to fight as her champion. Tyrion also demands the right to name a champion to fight on his behalf. Ser Vardis agrees that because Tyrion is a dwarf half his size and thus not martially skilled, it would be shameful to kill him and call it justice, and he gladly accepts to fight Tyrion's champion. Tyrion initially tries to name his brother, the feared master swordsman Ser Jaime Lannister, but Lysa refuses and insists that the combat must take place that day. Tyrion asks for volunteers from the court but is only jeered at, however just as Lysa is about to condemn him, the common sellsword Bronn steps forward and says that he will stand for the dwarf.
Ser Vardis readies for the combat by donning full armor and a heavy shield. In contrast, Bronn eschews offers to be lent armor or a shield, preferring to maintain his maneuverability at the risk of making himself more vulnerable. The pair engage in a fierce running duel throughout the Eyrie's throneroom. Ser Vardis nearly forces Bronn out the Moon Door to fall to his death at one point, but Bronn breaks off from the attack. Bronn uses underhanded tactics such as knocking objects onto the floor, jumping over railings, and running behind stone pillars. This forces Ser Vardis to chase after him while still in his heavy armor, tiring him out. When Bronn sees that Vardis is tiring he seizes the opportunity to land a quick stabbing blow to his side. The wounded Vardis fights even slower, until ultimately Bronn quickly sidesteps him and slashes him deeply across the back with his sword. Bronn then disarms the badly wounded Vardis and having won the combat, finishes off Vardis by stabbing him in the neck with a sword, then throwing his body out the Moon Door in the floor. Lysa Arryn angrily shouts that Bronn does not fight with honor, to which Bronn matter-of-factly agrees, then indicats the Moon Door he had just thrown Vardis' body into, and points out that he fought with honor and died. Tyrion is then released as per the results of the trial by combat.
In the books
In the A Song of Ice and Fire novels, trials by combat are risky gambits only invoked when there is little other choice. In historical times there were more variations of the trial, such as a trial of seven when the two sides would pick seven champions who would fight until one side yielded or the plaintiff withdrew their charge. This was held to be a more holy contest, but the practical difficulties have made such trials rare. Ser Duncan the Tall first came to the attention of legend by holding a trial of seven against his accuser, Prince Aerion Targaryen, and defeating him and his seven.
- Trial by combat on Wikipedia.org.