You are so lucky that he bit the nice neighbor and not a stranger that would of called the cops of animal control. Poor Finn there must just be something about her that he feels he has to be defensive about. I too would have the vet check him out....maybe there is a deeper issue here. Did he act like he was in trouble when you reached him after he chased the neighbor home???? him only being 1 I just find this so odd and strange he would do this especially with no prior anger issues. Does she have a dog??? Maybe he got a bad scent from her or maybe she was afraid of him before this happened and he sensed that???? I feel for you. This problem is something that is hard to fix and to understand! Keep us updated!