"Killing" at a Green Day concert?

My friend was telling me that at a '09 Green Day concert in Nashville, TN there was some sort of thing where they acted like they were killing some kid. She mentioned something about how it was an Antichrist sort of thing. Does anyone know what she is talking about. She heard it from another friend who was actually at the concert. I just want to see if i can figure out what really happened. Any help would be appreciated! Thanks!