Wiktionary
low blows
n. (low blow English)
Usage examples of "low blows".
Perfect backstabs and low blows, the most of those killed by the sword.
This bout was proving to be well worth the entrance fee: fierce fighting and fiercer words, high drama and low blows, a sibling rivalry with teeth in it.
So Hop used a few of the low blows he had learned in his childhood in the lowest corridor of Capitol, and Fritz was out for the duration.
Indeed, you may recall that after the 1992 General Election, when his newspapers were accused of some very low blows in their campaign coverage, it was hinted by Labour sources that were they ever to win power, his would be one score they would not forget to settle.