The area directly in front of the main stage at Edgefest was fenced off, and you needed special access to get in. So the kids pressed against its boundaries all day, standing against the gate and designated lines to get a few feet closer to the stage, still a third of a soccer field away.
A hole opened in the gate at the start of Paramore's set. I don't know why the security guard pulled it apart -- he did it just for a moment and turned his head and the kids started pouring through in one solid mass like a lake through a crumbling dam.