starting gate

noun2

1. •
   A machine used to ensure a fair start in horse or dog racing by opening doors to allow all the racing animals out at the same time.

   • Mobile starting-gates and horse-boxes stand parked along the kerbs, and behind every large house, it seems, is a red brick stableyard, gleaming with fresh black-and-white paint and polished steel. — 1980
2. •
   (figurative) The beginning.