The setup creates a stadium crowd. The rotating cheer_bbox object is used as a bounding box for the agents. When they are inside the bounding box it will trigger a transition from a sitting to a cheering state. After a few seconds the cheering crowd sits back down by transitioning into a sitting state.
To only see a section of the crowd for quicker preview there is a switch node in
/obj/crowd/switch_isolate. When 0 it will show all agents, and when set to 1 it will only show a small section.