Yep you can get the message over to your opposite number without having to play dirty. If you knee somebody in the nuts you need to be arrested. Play hard and make sure you go over to get your oppo a beer afterwards, a very civilised game. I was a back and once got co-opted to play in the scum, what a frightening place that was, the opposite prop looked at me, we locked heads, and he picked me up by the stubble on his chin. Never went back in there by choice ever again.