Most people forget that the brain is very soft. It has been compared to the consistency of soft butter, custard or tofu. And of course it is cradled in a skull that is very hard. So it dos not take much of an imagination to visualize what happens to the brain when the head hits something hard. Damage occurs and over time repeated injuries lead to permanent loss of function. The brain was not meant to hit a soccer ball or be put in a helmet and rammed into another person. The difference in PET scans of football players brains compared to people who have never participated in contact is quite remarkable. The destruction of brain tissue in football players is obvious even to the untrained eye.