A Wiffle ball with curve to the left for right handers and to the right for left handers. It is possible to get a two foot curve depending upon skill and practice. See the wiffle ball videos category for examples.
The ball must be a genuine Wiffle brand ball. Try not to use a brand new ball; with some coarse sandpaper, scuff the entire surface of the ball up to make the surface rough all-over. A smooth untouched ball simply won’t curve nearly as well and with as much ease as a roughed-up one.
A chair or some other flat surface should be placed where you would throw. In an actual game of wiffle ball a “strike-out zone” is placed beyond the batter. If the pitched ball hits this zone it’s a strike. The back of a lawn chair could be an ideal strike zone. The chair becomes a target for pitching and also serves as a stationary object tocompare the curve of the ball with.
Step One: The GripEdit
Whether left or right handed, hold the ball with the middle finger along the seam (the line right in the middle of the ball that separates the solid and perforated hemispheres) and your thumb also along the seam directly opposite of your middle finger.
The index finger should lie next to the middle finger comfortably. All of the holes must be facing the ring and pinky fingers.
Step Two: The throwEdit
Start by trying just a standard overhand throw and experiment with it. When releasing the ball, gently bend the wrist downward. Most of the force applied to the ball should be applied through your middle finger.
The first curve may appear within a few minutes of practice, however, perfecting and enlarging the curve will take a few days.
To throw a curveball with a taped up wiffle ball, grip the ball like a 4-seam fastball, but put the two top fingers together. Then upon the throw, snap the wrist and elbow over the top of the ball. It will sink and curve.
To throw a slider just grip a taped up wiffle ball like a 4-seam fastball and throw it side arm. Get the ball to spin like the Earth. The ball will curve a lot and may rise a little.