The Collaborative International Dictionary of English v.0.48:

Mumbledy peg \Mum"ble*dy peg`\, Mumblety peg \Mum"ble*ty peg`\,
   n.
   A game played with a pocketknife, the object of which is to
   throw the knife in any of a vairety of ways (such as over the
   back), or from various positions, and have it stick in the
   ground or another surface. Also called mumble-the-peg and
   mumble peg.
   [PJC]

WordNet (r) 3.0 (2006):

mumble-the-peg
    n 1: a game in which players throw or flip a jackknife in
         various ways so that the knife sticks in the ground [syn:
         mumblety-peg, mumble-the-peg]