starting block

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

• noun An apparatus that braces a runner's feet at the start of a sprint, consisting of two angled supports adjustably mounted on a rigid frame that is usually anchored to the track.
• noun One of the raised platforms mounted at one end of a pool from which swimmers begin a race.
• noun The beginning of an endeavor or period of time.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun block providing bracing for a runner's feet at start of a race