Liberal Dictionary English Dictionary
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.
When you are hit below the belt | THE GOSPEL TRUTH
English Weekly Idiom : Hit below the Belt – Liberal Dictionary
Hit below the belt » Liberal Dictionary
65) hit below the belt