This is the official full movie, The Purge Anarchy. One day a year, the citizens are unleashed to run amuck and kill. There are no rules other than you start killing when the announcements are made, and stop when the alarm sounds. Super villains like those in the official movie trailer for Suicide Squad LOVE this. Anyone who fires a shot after the appropriate killing schedule can and will be arrested for murder.
That may not make a lot of sense, but this is considered a cleansing. The purgers run around the city killing random or chosen individuals. Some dress in costumes, others just dress in everyday clothes. This official full movie shows it is kill or be killed during the Purge... like many super hero movies... unless you have a great place to hide.
Some individual hide out during the Purge to avoid being counted among the dead. This is not the time of year for the pacifist. Things get even crazier in the 2016 official movie trailer for The Purge, Election Year.