false start

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An illegal racing start in which one of the competitors begins moving before the starting signal.
• noun A violation of the rules governing the start of play in which a player moves from a set position before play is initiated, especially a rule violation in football in which an offensive player other than the center moves from a set position before the ball is snapped.
• noun A misguided or unsuccessful attempt to begin something.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun sports The starting of a race before being signaled to do so.