A poster-diagram of ‘the pit’ from heavy a metal concert that defines the different areas and the unspoken rules that exist around it, such as…
Front row/on-the-barrier, about 2 or 3 people deep, un-moving.
Behind that - the main pit. An area of non-specific size (ebbs and flows in size and dynamic throughout the gig). The main rule - if someone falls, you help them back-up immediately.
On the edge of that - the pit-guards. A self-selected row of people, one-person deep, who act as a barrier between the pit and the people who just want to stand and watch. These people play an active role in, both, defending the standers from the pit, and also pinballing wayward pit members back towards the centre of the action. Pit-guards often peel-off into the pit for a while, then rejoin the row of pit-guards.
Behind that, the standers. The people who just want to stand and watch to enjoy the gig. Secondary rule - don’t start a new pit amongst the standers; make your way to the main pit and join in.
Etc. etc.