How much does rule changes "to make the game safer" contribute to this?
http://www.espn.com/nfl/story/_/id/24177013/baltimore-ravens-coach-john-harbaugh-says-rookies-tough-were-past
http://www.espn.com/nfl/story/_/id/24177013/baltimore-ravens-coach-john-harbaugh-says-rookies-tough-were-past