Throw this pitch with the same arm speed and body mechanics as a fastball, only slightly turn the ball over by throwing the circle to the target. This is called pronating your hand. (Think about this as giving someone standing directly in front of you a "thumbs down" sign with your throwing hand.) This reduces speed and gives you that nice, fading movement to your throwing-arm side of the plate.
Another property of pitches is their break. Most commonly, that is the difference between their trajectory and that of a ball thrown with the same initial velocity, but no spin. As you may recall from earlier articles in this series, a basic fastball breaks up, while a basic curveball breaks down. A pitcher’s arm angle can modify these motions, so that a righthanded pitcher’s (RHP’s) fastball moves tends to move toward third base, as well as up.
Grip the ball. The knuckle curveball is similar to other grips, but the variable this time will be your index finger. Grip the ball with your middle finger along the bottom seam, and your thumb along the back seam. Hold the baseball such that the curves of the seams are close to your palm, with one on top and one on the bottom of your palm. Bend your index finger inward before laying it on the ball so that your nail and top knuckle are resting on the ball and your middle knuckle is pointing at the target.

So, when their focus is on adding extension to the delivery and trying to “reach out”, trunk rotation suffers. Because the pitcher is focused on arm extension (the idea of “reaching out”), his body exaggerates that action and forgets that upon landing the trunk must begin rotation followed by flexion in order to maximize all transferred energy so the arm gains maximum velocity.
Hold the ball so that the u shape is facing you upside down.  If you are a righty do it like this.  Placed your middle finger of you right hand onto the right seem of the upside down u.  place your pointer finger directly beside it.  Place your thumb on the seem on the other side of the ball on the left seem.  Place your ring finger on the bottom of the ball curled up with the pinkey finger beside it.  The pinkey finger should not touch the ball. Here is a picture of the grip.

Every pitcher wants to learn how to throw a curveball. Why? Because it’s effective and it gets hitters out. There’s nothing like throwing a curveball that makes a hitters knees buckle. It’s a great pitch to have in your arsenal because hitters never really learn how to hit a curve or adjust to it. Hitters can hit a good curveball but they can’t hit a great one. Even the greatest of hitters struggle hitting it; they just hope they don’t miss the opportunity to hit a fastball when it comes.
Now, the "markings" he will have on the mound should create an imaginary letter "H" if one looks from the side. The pitcher then goes through his entire delivery (with or with out throwing the baseball at the end of the motion) and looks to see where his front foot lands in relation to the two lines he has etched out in the dirt. He can use either his full or set wind-up in this drill. Did the pitcher land the length of his height? Did the pitcher stride in a straight line toward his target? If not, a pitcher should perform this drill 50-times a day without throwing the baseball.
3. Elbow: The throwing elbow must be equal to or slightly above the throwing shoulder. As soon as the pitcher lowers the elbow below the shoulder, they put additional stress on that arm. The angle of the elbow joint should be no more than 90 degrees. Pitchers who throw curveballs at angles greater than 90 degrees may put additional stress on their throwing shoulder.
[circle_list] [list_item]The drill should address and benefit at least two of these components (Balance and Timing, Timing and Power, Balance and Power, or all three).[/list_item] [list_item]The drill must not negatively impact any one of these components (for example, if a drill teaches balance, but hurts timing and power by having the pitcher pause and lose momentum, then it is counterproductive).[/list_item] [/circle_list]
This drill is a pitching drill in which the young pitcher works at a smooth, rather fast pace, but only throw 50-60%. He should not be allowed to throw full speed. The objective of the drill is to teach concentration and develop great control. The pitcher has to throw 20 strikes before he throws 4 balls. He should be allowed to perform the drill at a shorter distance at first but he should be able to move to his regular pitching distance within a couple of weeks. If he throws 4 balls, he must start over. Be careful to not overwork him. However, keeping the distance short, emphasizing accuracy not speed, and making sure he proper stretches and warms up should prevent any chance of arm injury. With younger players you may want to make the drill a 10-3 drill. He must throw 10 strikes before he throw 3 balls or he must start over.

When thrown, try to manipulate the pitch to come off of the thumb-side of your index finger – NOT your index- and middle-fingers, as with a two-seam fastball – because a two-finger release will cause the pitch to balance out, which reduces the spin that you are looking for. Most good slider pitchers grip the outer-third of the baseball and cock their wrist slightly, but not stiffly, to their throwing hand's thumb-side upon release of the pitch. This enables a pitcher to apply pressure to the outer-half of the ball with the index finger. Avoid any twisting of the wrist upon release.
In this video I answer some questions about the King of the Hill Pitcher’s Trainer, one of which was “what type of pitching drills can you do on the King of the Hill?”.  If you like the King of the Hill, and I definitely suggest this product for pitchers of all ages, then you can check it out at King of the Hill.  I really love this product because it teaches pitchers how to properly and efficiently get the most energy out of their legs.