Legends of the Broadsword: The Duel of the O'Connors
This was a formal judicial duel carried out at Dublin Castle in the year 1528 (or, according to one source, 1583) between two feuding cousins with the magnificent names of Connor MacCormack O'Connor and Teig McGilpatrick O'Connor. Adam Loftus, the Archbishop of Dublin, was one of the presiding Lords Justices in the case, along with Sir Henry Wallop.
According to Connor, Teig had killed some of his men who were under protection, by setting their house on fire and then cutting them down when they ran out. Teig agreed that he had, but maintained that the men were rebels and he was right to kill them. He was willing to maintain his innocence by force of arms, and the weapons he selected were the sword and target. Curious as it may seem, it was accepted legal practice at the time to prove yourself innocent of murder by fighting and killing your accuser, but Teig also accused Connor of treason and rebellion, and treason was considered a more serious accusation than murder in the first place.
Connor was apparently a "wild chief" of the Gaelic Irish, while Teig was only "semi-wild," which means nothing more or less than that Teig was relatively well-disposed to the English government and Connor was not. The sources on this duel are contradictory on several points, including which O'Connor was the victor in the fight, but what seems to have happened was this. The two men were stripped to the waist and searched for magic amulets and hidden knives, then sworn in formally and given their weapons. Teig (being the sort of fellow who would burn your house down, kill you when you tried to escape, and then happily admit it) was the better fighter, and he nicked Connor twice in the leg and once in the eye. In desperation, Connor charged, hoping to grapple with Teig and throw him down. Teig wrapped his arm around his cousin's neck, putting him in the position known as "head in chancery." He then bashed his pommel into Connor's face, continuing until he had "knocked the seven senses out of him." Connor slumped to the courtyard unconscious, and Teig immediately cut his head off and presented it on the point of his broadsword to the Lords Justices. As for the Englishmen watching this bloody spectacle, they are recorded as having wished the same fate upon "the whole sept of the O'Connors."
(Trial by Combat, by George Neilson, 1891, The Midland Septs and the Pale, by Francis Ryan Montgomery Hitchcock, 1908, Dublin Castle, by Maurice O'Connor Morris, 1889)