I thought Finrod had to convince them not to attack the men, as he lead the through Ossiriand.I thought the Green Elves fled, not attacked.
Now the Green-elves of Ossiriand were troubled by the coming of Men, and when they heard that a lord of the Eldar from over the Sea was among them they sent messengers to Felagund. 'Lord,' they said, 'if you have power over these newcomers, bid them return by the ways that they came, or else to go forward. For we desire no strangers in this land to break the peace in which we live. And these folk are hewers of trees and hunters of beasts; therefore we are their unfriends, and if they will not depart we shall afflict them in all ways that we can.'