I have been in that exact spot in that stadium and watched fans throw batteries at the opposing teams' cars, and all sorts of unsavory behavior.
Usually it's the opposing team, and usually fueled by alcohol.
This may be different... I know that East Bay fans aren't too pleased with rumors that the OL let Carr get smacked around because he stood for the anthem.
An anonymous source was quoted as saying:
"Stand alone off the field, stand alone on the field."