It's not that hard to adjust the pressure in those guns to dangerous levels. There must be a reason the fans of this sport in legitimate venues where heavy clothing, face masks, etc.
Since they were able to break a window, I suspect they did some tinkering with the guns.
and i dont think they needed to tinker with much considering that most paintballs go at what? 300-400fps? i think that house windows or car windows would probably shatter if hit close enough,
My opinion