It is called a "sucker punch" most commonly used by nigs who want to look tough but do not want to risk getting their ass kicked. Sucker punches can be extremely life threatening since the victims are unaware that they are about to be attacked often causing severe brain trauma and many times resulting in falls where the victim and hits their head on the pavement, like George Zimmerman.
Sometimes "sucker punches" go wrong though like in the case of Trayvon Martin where he lost his life for doing this in a state that gives victims of "sucker punches" the right to take the life of the coward who "sucker punched" them.