starting block

American Heritage® Dictionary of the English Language, Fourth Edition

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

WordNet 3.0

1. n. block providing bracing for a runner's feet at start of a race