I don’t know all that much about warfare in island Polynesia, so I’ll just very quickly go over a story or two first. In the second half of the 19th century the pastor Mamae (of Mangaia, the southernmost of the Cook Islands) recorded a story about one of his warrior ancestors, ‘Īkoke of Ngāti Vara. I’ll just post the translation (Michael Reilly, 2001) as my very poor reo Māori isn’t enough to get anything useful from the original.

Īkoke was a son famed in war. He was involved in a great battle in the time of his father and two elder brothers; he became well known. When the two older brothers died, he was involved in the battle at Tuāopapa. 'Āmai was the warrior of one group. They yelled war cries on the battlefield. 'Īkoke undid his loincloth and fearlessly praised his stick, that is, his penis, as his fighting weapon in front of the enemy. 'Īkoke asked that warrior ['Āmai] and those along in front to stab his penis: if [he] were wounded they would live, [but] if [he] were not wounded, he would slay the whole of [that] force.

That warrior stabbed at 'Īkoke with his spear. 'Īkoke dodged [the spear] and was not wounded. 'Īkoke put on his loincloth and slew that warrior and there was a great destruction from Tuāopapa right up to Te Rimu in Ivirua.

There was no warrior known in the whole of Mangaia who could show off that fighting stick. This was the name of that weapon, the hard penis [Te Ure mārō].

There are a couple of things that we can learn from this, but sticking with the relevant bits, we see that before the battle itself begins, people shout war cries and leaders engage in conversation and single combat. For this to be possible the main bodies must be hanging back. This would be when war dances could occur, and further evidence comes from the battle where it was mentioned that ‘Īkoke won fame, which was named ‘Arerā. The combined forces of Nāriki and Tepei had arrived at their chosen battlefield, and arranged themselves in ranks, then, as Ngāti Vara came into sight, performed a war dance (reru tāki).

Similar descriptions of pre-battle conversations and duels come from Tahiti. The missionary J.M. Orsmond wrote that

There is nothing more difficult than to make a foreigner see the force and beauty of the Tahitian war language. The Battles themselves considered apart were contemptible, but the power of imagination and the fire of speech were amazing.

As to how this situation could occur, I’m afraid I’m not entirely sure. The relatively low importance of missile weapons in Polynesia in general (particularly in East Polynesia) likely contributed though. The lines could assemble closer together than would be safe in, say, most of Melanesia, and charging into close combat with spears and clubs probably required more psychological ‘preparation’.