From the hand of a former major leaguer
Arm speed! Arm speed is utterly important with any off-speed pitch. The grip slows the velocity of secondary pitches. Think aggressive and think fastball when throwing secondary pitches.
Here are proper grips of six of the most commonly thrown pitches in baseball.
The typical MLB starting pitcher has three pitches: FB, curve or slider, and a change up - some have a fourth pitch, often being a cutter or splitter.
The typical MLB relief pitcher has only two pitches. Why? Beyond the sixth inning a relief pitcher will only pitch three to six outs and will only face the same hitter once.
It's not uncommon for a youth pitcher to state they have four or five pitches. This is unnecessary. Why have four or five mediocre pitches rather than two really good pitches? Be really good at throwing one pitch before moving onto another.
Four seam: Typically straighter and harder than a two seamer because of the way the seams cut through the air. Every youth pitcher should learn how to throw and command this pitch
Two seam: Typically has movement and is slower than a four seamer. What good is movement if you don't know exactly how the ball will move every single time you throw the ball (unless you're a knuckle ball pitcher, of course)? A good two seamer will be down in the zone and have movement towards a right-handed hitter (for a RHP) or have movement towards a left-handed hitter (for a LHP). It's not uncommon for youth pitchers to miss up in the zone when throwing this pitch. When the pitch is up, it tends to be flat and much more hittable.
Mariano Rivera anyone? A good cut fastball is less than five MPH slower than a four/two seam fastball and has late, lateral movement. This pitch should not have big movement but rather sharp, small, and late movement. Finger pressure is typically heavier on the middle finger at release and it's important to have your fingers on top of the ball at release, not behind or underneath.
The change should look just like a fastball out of the hand and should be eight to ten MPH slower than a fastball. A good fastball and change up is a devastating combo! Let the grip kill the velocity, not lack of arm speed. This pitch has to be down in the zone to be effective and fingers must be on top of the ball at release. It's not uncommon to see youth pitchers have their hand underneath or behind the ball at release.
The higher the spin rate, the better the break will be - arm speed! A good curveball will have close to a twelve to six movement shape and not pop upwards out of the hand when thrown. You want tight rotation. The middle finger is the dominant finger at release. We often see youth pitchers get on the side or underneath the ball to try and create break. You'll want to pretend you are throwing a hammer, wanting the handle and head of the hammer to rotate twelve to six through the air. Extension out front is critical. Did we mention arm speed?
We used to joke with some professional hitters we played with that their favorite pitch was a slider in the other batter's box.....because a good slider might be the toughest pitch to lay off of in baseball. This can be a tough pitch on the elbow so you'll want to make sure your mechanics are solid and be sure to keep your flexor muscles in your forearm strengthened. A good slider is thrown hard, four to eight MPH slower than a fastball, and has a late, two to eight movement (for a RHP). Your fingers must be on top of the ball and slightly around the ball at release. Think hard, think arm speed, think out front (extension).