You could describe the palmball as a curveball that is delivered off-speed, or an off-speed pitch that has a lot of motion. It is especially dangerous because the pitcher's motion will be identical to their fastball (including arm speed!), but the ball will come off at an odd angle, off-speed, and (hopefully) sink dramatically into the strike zone. It is probably the easiest way to put a lot of spin on the ball without the additional arm strain of the curveball or other breaking balls. Thus, it may be the most appropriate breaking-ball pitch to teach to young pitchers. My father taught me way back when I was in little league, and I ended up doing rather well with it.

The Grip

To grip a palmball, hold the ball diagonally across the seams with your middle finger and thumb, with the ball tucked against the palm of your hand and the webbing of your thumb. Use the seam of the ball for leverage against your middle finger. No other fingers should touch the ball - people mistakenly think "palmball" implies that you're fisting the entire ball like juicing an orange. In fact, touching the ball with your other fingers will upset the pitch. Just leave your other fingers slightly off the ball so you don't give away to the batter what kind of pitch you're throwing.

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The Motion

The motion for a palmball should be exactly like your fastball. Good hitters can pick up on the type of pitch from the pitcher's motion, so this is an exceptionally deceptive pitch, given its radical motion and how slow it comes off. The idea is to throw through the ball, using your arm speed to impart downward and outward spin to the ball rather than just forward velocity. Once you get the feel of the pitch, you shouldn't have to aim it any differently than a fastball - the pitch will just "home in" to where you're aiming. You can learn to throw this pitch harder or softer... a soft palmball will act like a good changeup or sinker, and a hard-thrown palmball can have a huge amount of motion on the pitch.

The Release

The release should be completely natural. Flick your middle finger down and to the outside of the ball at the point of release, in sync with your arm's motion. The ball should pop out at an odd angle, soaring high like a dramatic curveball, but slower. Experiment with the angle of your hand at release, it will affect the trajectory and motion of the ball.

Using it

The palmball is the perfect mix-up pitch for fastball pitchers - that is, everyone who hasn't adopted a specialty pitch. It's also a good addition to the repertoire of a variety pitcher. With practice you can confound your opponent with a wildly-sinking changeup that looks just like your hard fastball. Unfortunately it's probably not going to be the most accurate of pitches for you, so don't use it on a patient hitter when you're in the hole.

Note: many people refer to the palmball as a straight changeup, as opposed to a pitch with breaking action. To throw a straight changeup with a palmball grip, you can change the aforementioned grip in 2 ways. One way is to grip the ball between your thumb and the bridge of your palm, using your middle finger only to steady the ball. As you release, let the ball roll off your finger gently. The second way is to grip the ball exactly as above, only rotate the ball so that your middle finger is on the other side of the seam. This way the ball will slide out of your hand without your finger imparting all that spin onto it. These kinds of palmball will have some sinking action to them, but not as much and won't come off at such an odd angle.

Most major-league pitchers are better served using their curveball rather than a breaking palmball. Usually when you hear of a professional pitcher with a palmball, it is referring to the straight changeup variety.