When you're playing a game or performing some other skilled activity, and a loss of focus, distraction, stress, or any combination of similar factors results in a rapid and uncharacteristic loss of skill or finesse. You start making noob mistakes.
"He was playing well for a while, but then he made a mistake or two and started noobing out. He totally blew it at the end."
by binarymike July 08, 2011