I say neither, but at the same time it was dangerous for Cav to attempt to go between Sagan and the wall, but again, it's racing and you do some crazy things.
Remember back in 2010 when Renshaw was taken out of the tour for headbutting, but I thought he was just keeping the other guy from coming into his line. It seems like the officials just like to hate on those that are really successful.
Look at the video, yes Renshaw was head-butting, but the other guy instigated the whole thing.