I can find this phrase in a few dictionaries:
knock-down, drag-out — marked by extreme violence or bitterness and by the showing of no mercy knock–down, drag–out political debates
But I don't fully understand why these two phrases became such a common saying. Why did this particular combination come to mean a particularly terrible fight or war? Is there something in each phrase that brings a particular meaning? Or does it just something that sounds catchy?
If it helps, here are the notes from etymonline that points toward the 1800s as the time of origin:
"Drag-out" came to mean "violent fight" but almost 30 years after the phrase "knock-down, drag-out" was recorded. So why did the phrase include "drag-out"? What did it mean in the 1820s?