More like a group of griefers enter the server and keep invading other people's properties. When they get inevitably kicked out, they get pissed and start causing problems for everyone. Then the admin gets involved, but the group just continues to ban evade, using TNT cannons (which bypass zone protections), building lag machines, and luring creepers into people to explode them. Then some of them worm their way into VIP or even admin positions and start changing server policies to favor only them.