hit below the belt

Cultural  

1. To say something that is often too personal, usually irrelevant, and always unfair: “To remind reformed alcoholics of their drinking problem is to hit below the belt.” The expression comes from boxing, in which it is illegal to hit an opponent below the belt.

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below the belt, hit Idioms  

1. 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.

2. see below the belt.

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