I think Cousins could have slide around him, but if Posey had been 2-3 inches further towards the plate, he has no angle. As a player, running full speed and having to make the decision to hit him or slide around him based on a 2-3 inch window is asking a lot. He COULD have tried to slide around the backside of him, or he COULD have felt he either couldn't get there, had the wrong angle or whatever and went with his second option, lowering the shoulder and going for the front of the plate (which he's also entitled to do, and Posey WAS covering that area of the plate). Contact could have been avoided I think, but I see nothing wrong with this play at all.