pl. n. scrubs; v. to scrub, scrubbing, scrubbed
1. v., in general usage, to rub hard and fast with a brush or cloth, as when cleaning; from Middle English scrobben, poss. Old English *scrobbian or *scrybban “to scrub”; c. 14th century.
2. n., in gamerese, esp. video games, syn. of newbie; describes someone who is bad at video games, whether due to lack of experience or of talent; presumably c. 1991.
Addendum: From Urban Dictionary, the Oxford English Dictionary of the Internet: “The original definition is related to a person who makes a mistake in a video game, which is such a bad mistake that it is clearly wrong, yet they persist in making it. The term derives from Street Fighter II, to describe some players that were so bad that they would mash their hands across the control pad, an act known as ‘scrubbing,’ because it relates to scrubbing a car or other object with a sponge. Thus they were deemed ‘scrubbers,’ or ‘scrubs’ for short. Over time this term expanded throughout the gaming world, and then the real world, and lost its original meaning.”
Addendum #2: According to TVTropes.org, “a Scrub is a player of a competitive video game who adamantly believes that his or her ‘house rules’ should apply to everyone to promote his or her view of ‘fair play.’ If a scrub sees a move or strategy he doesn’t like (or can’t beat), he bans it (if only in his own mind), and complains that anyone who uses it is cheap.”