What is the X in X-mas?
1955, in nerf bars, hot-rodder slang for "custom bumpers;" from slang verb in auto racing (1953) meaning "to nudge something with a bumper in passing and knock it off course;" ultimate origin and signification unknown.
As a trademark name for toys made of foam-like material for indoor play, introduced 1970 (Nerf ball). By 1995 this had yielded a verbal sense of "to make less effective" (as a Nerf basketball is softer and lighter than the real thing).
To bump a car out of one's way
[1950s+ Hot rodders; origin unknown]