"Knock down drag out" is an idiomatic phrase, which means a fierce and intense fight or argument. You can use some synonyms to describe the same level of intensity. For instance, you can use phrases such as "all-out brawl," "heated exchange," "no-holds-barred," or "blazing row" to depict a similar meaning. Additionally, you can use words like "fiery," "volatile," "explosive," or "stormy" to emphasize the forceful nature of the conflict. Other similar phrases may include "knockout punch," "intense battle," "all-out war," or "violent altercation." Using these synonyms appropriately, you can vividly describe the intensity of a fierce fight or argument.