Pitching can be one of the hardest things to teach young players. Even if you have been a pitcher yourself, chances are you gravitated to pitching because it came very natural to you and never really had to think about every little detail. If you have never pitched, teaching a young player will be even more difficult.
A great guide to teaching the pitching basics is the book "The Picture Perfect Pitcher" by Tom House and Paul Reddick (2003). The authors break the motion into 5 absolutes of pitching: balance position, equal and opposite elbows, late rotation, blocked-off frontside, and finish. The photo to the left illustrates balance and blocked-off frontside. Many Little League pitchers don't always achieve these positions, which makes pitching very difficult.
The first absolute is balance. No matter whether the pitcher has a very flashy windup like Hideki Nomo, or a very slow deliberate windup like Nolan Ryan, they all get to the balanced position as shown in the photo at left. Balance is more than all your weight on the back foot. The front leg should be raised about waist level, and back as far as the rubber. The hips and shoulders should be cocked so that the batter can see the pitcher's numbers. This is the point most young players fail to reach. It is a little uncomfortable to almost turn your back on the batter. Also, the front foot should be relaxed and both eyes picking up the target.
Equal and opposite
The next absolute is pretty obvious. From the balance position, the pitcher separates his hands in a circular motion to get to the power position. At the power position, the upper arms are generally both parallel to the ground. However, the authors of the above noted book don't think it is required to have the arms parallel to the ground, just that the elbows and shoulders should be in a straight line.
A current major league pitcher that doesn't have his arms parallel to the ground is Andy Pettite. His front elbow is extremely high, but his back elbow is low to keep the elbow-to-elbow line straight. Dennis Eckersley was just the opposite. His back elbow was held high, but the front elbow stayed low.
The biggest problem seen in Little League is that the front elbow never gets high enough. Kids tend to not want to block their view of the target and get their arm out of the way by keeping the front elbow too low.
This simply means the glove comes to the chest, or chest to the glove, as shown in the photo at left. In an effort to throw harder, young pitchers will whip their glove around so that by the time they release the ball, it is down by their glove side knee, as seen in the picture at right.
Once the pitcher flies open like this, all that is left to throw the ball is the shoulder and elbow, therefore both assuming a good amount of stress. By flying open, the pitcher's momentum is no longer going toward the plate, so control is a big problem if the pitcher does not block off the frontside.
The final absolute is the finish. Sometimes this is called the follow through. Once the ball is released, the pitcher's body should twist so that the throwing elbow crosses the body and ends up on the outside of the opposite knee. To do this properly, the back has to bend, and the body extend toward the batter