Why would Green leave CS for Saosin? Saosin is pretty much irrelevant in the scene and Circa still has a pretty devoted following.
He wouldn't leave Circa. But from what I've heard, he wanted to sing aggressively again and was wanting TSOAF to do another record put since not everyone was on board, it seems he has joined saosin for this upcoming record. And it's strongly hinted since he joined two of the guys from Saosin recently on stage to perform 7 Years.