Instructions
Unplug the Wii remote nunchuk from the bottom of the remote controller. Do this while the system is turned on and a game using the nunchuk is loaded.
Set down the nunchuk with the joystick facing up. Make sure the joystick is directly in the central, neutral position and do not touch it. If the joystick is being held in a different position when you recalibrate it, it will recalibrate that position as the new neutral position. This can cause the controller to always move in one direction, such as left.
Plug the nunchuk back into the Wii remote controller, making sure the joystick is still in the neutral position. The controller will recognize the nunchuk and should reset it back to its original position.