It's a noun. Means someone who will defend or make excuses for someone or something that doesn't necessarily deserve it or is controversial.
In the context of this forum, it means an idiot or idiots who think we shouldn't go after players like Angus Crichton because we have Seyfarth. Or someone who thinks Nofoaluma deserves respect despite being a selfish clown who only cares about himself.
Does that clarify things for you or would you like me to get the colouring in book and crayons out for you?