An unfair and malicious stroke; cheap shot: ''They'd be rendered mute if they couldn't use sports analogies.'' ''Low blow, Alice''
[1940s+; fr the illegal blow below the belt in boxing]
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with low-blow
An unscrupulous attack; an insult. For example, When my roommate moved out without a word of warning, leaving me to pay the entire rent, that was a low blow, or She wanted to win the argument, but bringing up his failed marriage was a low blow. This term alludes to the illegal practice of hitting an opponent in boxing below the belt
[ c. 1950