Instructions
Press the "A" button after "Go" appears in the game to begin swinging the hammer.
Swing your controller, not the nunchuk, around in small circles. The faster you swing it, the more momentum your character gains.
Press the "B" button to release the hammer from your character's hands and onto the field. You must time the release so that the hammer is thrown directly in front of you between the nets. If you don't, then your throw will be ruled a "Foul."