below the belt, hit

Not behave according to the rules or decency, unfairly, as in Bringing up my mother's faults—that's really hitting below the belt. The term comes from boxing, where according to the Marquis of Queensberry Rules (1865) a fighter may punch his opponent only in the upper body or head. For a synonym, see low blow; also see under one's belt.

The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.