The Cattle Raid of Cualnge, by L. Winifred Faraday, , at sacred-texts.com
Then the Meic Garach waited on their ford. These are their names: Lon and Ualu and Diliu; and Mes-Ler, and Mes-Laech, and Mes-Lethan were their three charioteers. They thought it too much what Cuchulainn had done: to slay two foster-sons of the king, and his son, and to shake the head before the host. They would slay Cuchulainn in return for him, and would themselves remove this annoyance from the host. They cut three aspen wands for their charioteers, that the six of them should pursue combat against him. He killed them all then, because they had broken fair-play towards him.
Orlam's charioteer was then between Ailill and Medb. Cuchulainn hurled a stone at him, 1 so that his head broke, and his brains came over his ears; Fertedil was his name. (Thus it is not true that Cuchulainn did not kill charioteers; howbeit, he did not kill them without fault.)
38:1 Apparently because the charioteer had not carried Orlam's head into the camp on his back. Or an alternative version.