The Collaborative International Dictionary of English v.0.48:

knock-down-and-drag-out \knock-down-and-drag-out\,
knockdown-dragout \knockdown-dragout\adj.
   marked by extreme violence; -- of fights; also used
   metaphorically of fierce contests; as, a
   knock-down-and-drag-out fight; a knockdown-dragout
   competition for the browser market.

   Syn: ferocious, fierce, knockdown-dragout, tearing.
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

knock-down-and-drag-out
    adj 1: extremely violent; "a knock-down-and-drag-out fight"
           [syn: knockdown-dragout, knock-down-and-drag-out]

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "knock-down-and-drag-out":
   affray, altercation, barney, bickering, boisterous, brawl, broil,
   dispute, donnybrook, donnybrook fair, dustup, fight, fracas, fray,
   free-for-all, harum-scarum, hassle, knockabout, melee,
   rambunctious, rampageous, rhubarb, riot, roisterous, rollicking,
   rough, rough-and-tumble, row, rowdy, ruckus, ruction, rumpus,
   run-in, scrap, scrimmage, set-to, shindy, wild