Fintan, himself the son of Niall Niamglonnach ('of the brilliant Exploits') from Dûn da Benn, was father of Cethern son of Fintan. And he came to save the honour of Ulster and to avenge his son upon the hosts. Thrice fifty was his number. And thus it was they came, and two spear-heads on each shaft with them, a spear-head on the top and a spear-head at the butt, so that it made no difference whether they wounded the hosts with the points or with the butts. They offered three battles to the hosts. And thrice their own number fell at their hands, and there fell also the people of Fintan son of Niall, all excepting Fintan's son Crimthann alone. This one was saved under a canopy of shields by Ailill and Medb.

Then said the men of Erin, it would be no disgrace for Fintan son of Niall to withdraw from the camp and quarters, and they would give up Crimthann son of Fintan to him, and then the hosts would fall back a day's march to the north again; and that he should cease from his deeds of arms against the hosts till he would come to encounter them on the day of the great battle at the place where the four grand provinces of Erin would clash at Garech and Ilgarech in the battle of the Cattle-reaving of Cualnge, as was foretold by the druids of the men of Erin. Fintan son of Niall consented to that, and they gave over his son to him. He withdrew from the camp and station, and the host marched a day's journey back to the north again, to stop and cease their advance.

In this manner they found each man of the people of Fintan son of Niall Niamglonnach and each man of the men of Erin, with the lips and the nose of each of them in the teeth and tusks of the other. The men of Erin gave thought to that: "This is a tooth-fight for us," said they; "the tooth-fight of Fintan's people and of Fintan himself." So this is the 'Tooth-fight' of Fintan.