off and running - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Making a good start, progressing well, as in After the first episode the new soap opera was off and running. Originating in horse racing, as the traditional announcement at the beginning of a race (“They're off and running”), this phrase began to be used more broadly in the second half of the 1900s.