How many metallica fans does it take to cause a riot

There was rioting in Bogota last night outside Metallica's gig there: http://www.nme.com/news/metallica/50193
As I looked into this it soon be became apparent that the words riot and Metallica are often snuggled close in newspaper headlines.
Chile and Columbia is understandable, lifes not always great, people get pissed off when they can't get those things as basic to human need as food or a ticket to a Metallica show. But what about Sydney? Or even more incredible, the band even had it all kicking off in decent and mild mannered Canadia's second biggest city, Montreal.
Obviously Metallica didn't cause these riots themselves, they were on their private jet doing yoga stretches probably.
But they still deserve to be the Emperors of the Devil Horniverse