Douglas Harper's Etymology Dictionary
boys' knife-throwing game, 1650s, originally mumble-the-peg (1620s), of unknown signification and origin.
WordNet
n. a game in which players throw or flip a jackknife in various ways so that the knife sticks in the ground [syn: mumble-the-peg]
Wikipedia
Mumblety-peg (also known as mumbley-peg, mumblepeg, mumble-the-peg, mumbledepeg or mumble-de-peg) is an old outdoor game played using pocketknives. The term "Mumblety-peg" came from the practice of putting a peg of about 2 or 3 inches into the ground. The loser of the game had to take it out with his teeth. Mumblety-peg was very popular as a schoolyard game in the nineteenth and first half of the twentieth centuries, but with increased concern over child safety the game has declined in popularity. Mark Twain's book Tom Sawyer, Detective recounts "mumbletypeg" as one of boys' favorite outdoor games.
Usage examples of "mumblety-peg".
They love to eat and drink, play mumblety-peg with dim-witted quadrupeds, and tell off-color dwarf jokes.