There is a bit of mythology here and other cities have bad fans as well.
They claim they did not boo Santa Claus, that his sleigh had an advertisement on it and they were booing the commercialization of Santa.
They also threw snow balls at him.
I've worn my Pirates' gear in the home stadiums of many hated rivals including St. Louis, Cincinnati and Chicago and never felt the least bit unsafe. In NYC, on the Lex up to Pelham to the South Bronx and on many trips over to Flushing I have never felt anything but goodwill from Yanks and [much more often] Mets' fans. Not so -- EVER -- in Filthydelphia, and I've been going to games there since Connie Mac Stadium.
Philadelphia's legendary lack of sportsmanship is no myth. They're the worst fans in the country. Period. No other team that I know of has ever installed a District Magistrate and a jail in their facility. Do you know of one?
Western PA hates Eastern PA for a reason. Philly should be called West Camden, and annexed to "The Garden State." They'd be much more at home there.