Hi Smeagol! I know this phrase because we use it in spanish for say that someone is defending someone else who has acted wrongly. For example, I am in a discussion between a man and a kid who has broken a window because he hit it with a baseball bat. I will play the rol of devil's advocate if I defend the kid, because you can't defend something not defensible, he broke the window because he wanted it and that's all. I don't know if I explain me fine. Hope this help you!