Person put forward new rule in overbearing manner after taking sides (7)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

I need help here: it was only at the point of posting that I realised that I hadn’t managed to untangle all the parsing here, so, rather than delay the blog, I’ll hand over to you. Thanks to everyone for the help: I had a real blind spot there. N (new) + [d]OMINEE]r] (rule in overbearing manner) taking ‘sides’ away