My parent went to SF to see the Bills play recently and I was actually very nervous for their safety. But luckily no incidents, just some minor harassing in the parking lot.
From my own experience, I have been confronted in Baltimore, Chicago, Cleveland, and Indianapolis. But I didn't act like a d*ck and was smart enough to realize I was severely outnumbered and simply walked away. There are idiots at every stadium, there is no such thing as a zero incident stadium...