What is another word for put/stick the boot in?
Pronunciation: [pˌʊt slˈaʃ stˈɪk ðə bˈuːt ˈɪn] (IPA) 
The phrase "put/stick the boot in" is a colloquial expression used to describe someone who is aggressively and relentlessly attacking another person, either physically or verbally. There are a variety of synonyms for this phrase, including "kick someone while they're down," "pile on," "ganging up," "barrage," and "blitz." Each of these phrases describes the act of someone who is continuing to attack or harm another person even when they are already in a vulnerable position. Whether it is in a physical altercation or a verbal argument, these synonyms accurately capture the intensity and brutality of the phrase "put/stick the boot in".
