As Aiwendil says,
I'd guess that this refers to some 'chess-like' game. Indeed the Prof's beloved Anglo-Saxons, the Norse and Celtic nations all apparently played some variant of the 'Tafl' game.
Interesting wiki page here
http://en.wikipedia.org/wiki/Tafl_games
For Pratchett-readers, the game Thud was inspired by these.
No idea if the hobbits ever played 'Cripple Mr. Onion' or sang a song about what's on the end of a wizard's staff though!