
1) Not fair 2) Slang for underhand, spiteful 3) Unfair 4) Unscrupulous or unfair 5) Unsportsmanlike
Found on
https://www.crosswordclues.com/clue/below-the-belt

Mainly used in combat sports such as boxing and kickboxing, below the belt refers to all the area of the body that lies below the line of the opponent`s navel, including the genital area, legs, and crotch. In these sports, as in many others, punches must not be struck below the opponent`s navel, as it is deemed unfair and contrary to sportsmansh.....
Found on
http://en.wikipedia.org/wiki/Below_the_belt

Below the belt meaning unfair comes from the unfair and illegal boxing maneuver of hitting someone in the nether regions. The phrase gained its figurative meaning around 1889.
Found on
http://mentalfloss.com/article/63958/15-common-phrases-come-boxing

Below the belt is an imaginary line from the belly button to the top of the hips where a boxer is not supposed to hit. To hit below the belt is to not behave according to the rules or decency.
Found on
http://www.encyclo.co.uk/local/21157

Below the belt is an imaginary line from the belly button to the top of the hips where a boxer is not supposed to hit. To hit below the belt is to not behave according to the rules or decency.
Found on
http://www.encyclo.co.uk/local/21482

Below the belt is slang for underhand, spiteful.
Found on
http://www.probertencyclopaedia.com/browse/ZB.HTM

[
adj] - disregarding the rules (from the notion of an illegal low blow in boxing)
Found on
http://www.webdictionary.co.uk/definition.php?query=below%20the%20belt
adjective disregarding the rules (from the notion of an illegal low blow in boxing); `her accusations were below the belt`
Found on
https://www.encyclo.co.uk/local/20974

Below the belt is an imaginary line from the belly button to the top of the hips where a boxer is not supposed to hit. To hit below the belt is to not behave according to the rules or decency.
Found on
https://www.encyclo.co.uk/local/21628

often used a metaphor for something unacceptable or uncalled for, in boxing refers to the illegal punch area, typically below a line, often dictated by the boxers shorts and abdominal guard.
Found on
https://www.encyclo.co.uk/local/23398

A punch that strays low, below the waistband of a boxer?s trunks.
Found on
https://www.titleboxing.com/boxing-dictionary
No exact match found.