An unorthodox strategy in chess consisting of threats of violence after the game.

From Star Wars, episode IV ("A New Hope"):

"It's not wise to upset a Wookiee."
"But sir, nobody worries about upsetting a droid!"
"That's 'cause a droid don't pull people's arms out of their sockets when they lose. Wookiees have been known to do that."
"Artoo, I suggest a new strategy. Let the Wookiee win."

Needless to say, the Chewbacca defense is barred under international chess rules.