Again, with the bunh of drunks and violence preconceived ideas. Those guys would create spectacular displays, before they could even attempt creating any disturbances. I might not be familiar with North American mentalities, but I think the movement could become very popular, at least in it's early stages. The working class could easily relate, and also the youth might be drawn to it, just like in Europe.
My dad brought up a good point by the way, there is no way you are bringing flares into a baseball game. Thats just not allowed. Also Baseball is a very calm game, people go to relax, sit back, and watch the ball game. If you want a sport where fans can get really raucous, Hockey might be your game, but even then its a stretch.