start in on
Begin doing something, as in We started right in on the repairs. Also see start in.
Attack, especially verbally, as in Nancy keeps starting in on Carl, complaining about the errors in his work. [Early 1900s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.