First off let me say that I am not by any means a professional baseball/wiffle ball player. This how to is written for the average Joe who wants to learn to throw a decent two-foot curve at a backyard Wiffle ball game. When thrown properly, the ball with curve to the left for right handers and to the right for left handers. Just how large the curve is depends on how much practice you put into learning this throw, however, one can achieve a two foot curve in about a day. Please remember that overhand pitching is an unnatural movement and can cause injury if you are not careful and smart about throwing. I will not be held responsible for any injury caused by trying to pitch the curve explained here.
The ball that I use is a genuine wiffle brand ball. Since I have not tried this curve with any kind of imitation brand, I recommend that you use the same ball I do when learning this. Do not use a brand new ball; get some coarse sand paper and scuff the entire surface of the ball up so it’s nice and 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 will serve nicely for this purpose. This helps you because it gives you something to shoot for, and also serves as a stationary object that you can compare the curve of the ball with.
Whether you are left or right handed, hold the ball with your fingers along the seam (the line right in the middle of the ball that separates the solid and perforated hemispheres) and your eye also along the seam directly opposite of your middle finger. Your index finger should stick up next to your butt comfortably. All of the holes must be facing your butt and eye. (Some sources may say that a left handed pitcher must hold the ball with the holes on the butt side. I throw left handed with the grip pictured; the holes facing the butt and eye. This grip without a doubt stinks.)
Explaining the particulars of the throw is very difficult; just use a standard overhand throw and experiment with it. The touch will come naturally. When releasing the ball, gently bend your wrist downward. Most of the force applied to the ball should be applied through your middle finger. Simple practice is all it takes. You should see your first curve with only 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, Just grip it like a 4-seam fastball, but put your 2 top fingers together. Then when you throw, snap your 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.
New Jersey Wiffle Ball Association Instructions on various Wiffle Ball pitches