Depends. Depends on how many brain cels you had to start with, on how hard the punch / blow was , on what part of the brain was hit ( and sometimes there's damage on exactly the opposite side of the brain, as it is bounced back against the other side of the skull ), on whether there has been previous brain damage, and so on. And part of the trouble with bozers' brains is the repetitive nature of the injuries --- maybe no one would have caused noticeable damage, but repeated head injuries, over a long period, can cause substantial damage