5Kennedy, Patrick. Legendary Fictions of the Irish Celts. London: Macmillan and Co., 1866. 183.
In legend, Oscar's "battle-rage" was so intense that "in his fury he also slew by mischance his own friend and condisciple." (Rolleson, Thomas William. Myths and Legends of the Celtic Race. London: George G. Harrap, 1949. 260-61.)
From Ferguson's introduction to his poem: "Oscar was entombed in the rath or earthen fortress that occupied part of the field of battle, the rest of the slain being cast in a pit outside."