The guy in that tweet probably got punched, knocked out, and hit the pavement with his head. The blow on the pavement can cause extra-dural bleed which may kill or cause brain damage due to the resultant increase in intra-cranial pressure - if is isn't relieved quickly by an operation that involves drilling a hole in the skull to let the collection of blood out.
Usually the person who delivered the punch gets charged with manslaughter if they die, or even murder. But usually a resultant conviction is for manslaughter.