There is a movie called “Purge”?
I don’t think knock-out assaults are involved here, as I am pretty sure that there are not white victims.
At the Six Flags in our town during one fright fest thugs started a fore at one end of the park to cover a fight at the opposite end
Apparently there was and this was hoaxed in July and August spreading by social media that REAL LIVE purges in which you could commit any crime for 12 hours and get away with it.
This “movie” was from 2013. Sequel in the works IIRC.
http://en.wikipedia.org/wiki/The_Purge