The Gorn destroyed the Federation outpost on Cestus III, and the pursuit that followed led the Metrons to force Kirk and the Gorn captain into single combat.
In 2267 the Enterprise arrived at the Earth outpost on Cestus III and found it destroyed, with a lone survivor and a Gorn ship waiting in ambush. Kirk chased the attackers, believing they were preparing an invasion. The pursuit carried both ships into the territory of the Metrons, who stopped them and placed Kirk and the Gorn captain on a planet to fight to the death, promising to destroy the loser's ship.
Kirk learned that the Gorn considered the outpost an intrusion into their own space. He built a crude cannon from minerals found on the planet and defeated the Gorn but refused to kill him. The Metrons, impressed by his mercy, spared both ships.