Have to say I'd love to know where some of these versions come from. The Celtic Folkweave and Bothy Band versions are unusual in that they start the story right in the middle of the battle, and I can't find any other versions that do this, or find the original source of that version.

There's a great collection of different versions and analysis here, and going through all of them I see a few variations but none in which the lyric starts with the fight.