Events are subject to requirements under public law, i.e. certain governmental retsrictions and controls. The scope of regulations which could play a role in the planning of an event is often manifold: From the right of assembly to building laws and trade regulations to restaurant and road laws and regulations. Also important are environmental laws and sanitary systems.
All of these provisions have one thing in common: They serve the protection and safety of the individual (e.g. visitor) and of the general public (e.g. subcontractor).