What is the origin of the idiom "below the belt" and when to use it?

The origin of the idiom "below the belt" can be traced back to the sport of boxing. In boxing, there are rules and regulations that define legal and illegal target areas for punches. Striking an opponent below the beltline, specifically hitting the groin area, is considered an illegal blow and is penalized. It implies that someone is hitting or attacking another person in a way that is unfair, unethical, or taking advantage of their vulnerabilities. Over time, the phrase has been adopted and used in various contexts beyond the world of boxing to describe any action or remark that is considered unfair or exploitative.