Because people from SF go to LA and start running their mouths at some dangerous people. I’ve been to dozens of Ram games since about 1966. The same thing happens in every city. If you don’t know better than to be polite in your Bengals jersey in Pittsburgh (eg). - you’ll probably get your head kicked in there too
Libertarians want to be left alone so I for one don’t wear jerseys to games-colors maybe. Lefties are more in your face with their opinions so they’re more likely to cross the line, especially after a couple of beers. Tailgating should be banned. Too much enclosed fun in minimal space where too many cars move around. Out here on the west coast a younger fella can down some rich food and waddle into the stadium before 1pm start time. Too much volatile pretend fun.