to duke it out

from The Collaborative International Dictionary of English v.0.48

duke \duke\ (d[=u]k) v. t.
   To beat with the fists. [slang]
   [PJC]

   {to duke it out} to fight; -- usually implying, to fight with
      the fists; to settle a dispute by fighting with the fists.
      See duke, n. sense 4.
      [PJC]