I didn't see much of Macca at Wakey so I don't know what type of game he played.
However in an interview he gave after he was added to the elite England training squad he was asked what had caused his game to improve so much at Cas. He said he had a chat with Powell and said he only wanted to play in a team who would let him play his own style of rugby and Powell said with a couple of tweeks he could accommodate that style of play into the Cas structures.
I'm only guessing but maybe he's playing well because he's enjoying it although when he first came he was behind Milner in the pecking order. Milner now converted to 13 to get them both on
the pitch for close to 80 minutes a game.
