The runner on third base starts home as the pitcher delivers the ball WordNet 3.0 & Open English WordNet

A play by the team at-bat where with a runner at third base, the batter puts down a sacrifice bunt with the aim of allowing the runner to score. In contrast to a safety squeeze, the runner sets off from third as soon as the pitch is made, allowing him or her to start running much earlier than on a safety squeeze. Wiktionary