This means immediately; at the very beginning. It describes a sprinter blasting out of the starting blocks at the beginning of a short distance race (e.g., 100-yard dash, 50-yard dash).
An blocks idiom dictionary is a great resource for writers, students, and anyone looking to expand their vocabulary. It contains a list of words with similar meanings with blocks, allowing users to choose the best word for their specific context.
Dictionary of similar words, Different wording, Synonyms, Idioms for Idiom, Proverb blocks