It's not normal but it's not abnormal either. You can find shitty fans of any team doing shitty stuff all the time.
Huge fight between Raiders and Niners fans
Two White Sox fans attack a Royals coach
Canucks fans riot after losing Stanley Cup
Giants fans throw snowballs and knock out a Chargers equipment manager
Oh, and there's the death threats Bill Buckner and Steve Bartman got from Red Sox and Cubs fans respectively.
The only thing one fanbase has in common is that they all cheer for the same team and they're all humans. Generalizing people by what team they cheer for is ridiculous, there's literally no commonality outside of the jersey on their back. Oh, and while you're sitting here bitching about Philly fans, a ton of apologetic ones were donating money to Mike Zimmer's charity to make up for the select minority of their fanbase who they felt were disrespectful. Blaming a whole group of fans for one stupid minority is ridiculous.