Knockout is the latest craze to come out of Black American subculture. Blacks attack unsuspecting passer-by (predominately whites) with the aim of KO them with one punch.
No doubt the usual angry black faces will find every one else to blame except of course the perpetrators (black Americans), but its worth remembering that slavery was abolished in the USA in 1865, so no black American has been affected by it. In fact, most black Americans are not even descended from North American slaves. More are the descendants of sub-Saharan slave traders and cannibals. More importantly, blacks have had equal legal voting rights with whites in the US since 1870, which is a lot earlier than the most white men and women in Europe.
Obviously racial prejudice still exist but its a two-way street, and certainly today more whites are attacked, raped, murdered, robbed or burgled by blacks than vice versa. The problem is that for far too long blacks American self-identity has been wrapped up in the culture of victimhood, and this is used as a justification for violence against white Americans.