the skull there are rough edges. and the brain hits the skull, and as it moves, literally the rough edges are tearing the fibers of the brave. so the concern is that can lead to damage that can last days, weeks, months and years. some of the symptoms, and you heard alison talk about it. they have headaches, difficulty concentra concentrating. vision and balance problems. extreme cases depression and decide. and the brain injury, and that's what they're calling this, a brain injury can last for some time. concentration problems, and so the recommendations that doctors are giving right now now is, listen, if you suspect that a player has a heads injury, stop there. get the player off the field at that point. do not put the player back on the the field until he or she has been evaluated by a doctor. not an e.m.t., a doctor who wants to check for head injuries. >> often the second and third hit will be turn out to be