The Ushaan is an Andorian tradition which means 'intimate' or 'private' combat that was developed in the planets brutal violent past. It was created by the Andorian reformist Lor'Vela who created this trial of combat to settle the matters of honor through combat between two individuals. This trial ended with the death of one of the combatants.
The Ushaan also covers the body of rules and regulations that govern this trial of combat which had 12,000 amendments made even after its original creation. One of these ammendments allowed for the right of substitution should the one being challeneged was unable to fight. Another ammendment to the code allowed a married combatant to postpone the trial by combat indefinately should they have no children. Though the trial originally was ended through the death of one of the combatants, should one of them be disabled in the fight then that would suffice as fulfilling the rules of the Ushaan.
Humans first encountered the Ushaan ritual when Commander Shran of the Andorian Imperial Guard challenged Tellarite ambassador Naarg. At the last minute, Naarg's role was substituted by Captain Jonathan Archer who fought in the ambassador's place. Combat ended when Shran's antenna was severed by Archer, fulfilling the rules of the Ushaan without killing Shran. (ENT episode: "United"; Last Unicorn RPG module: The Andorians: Among the Clans)