When most coaches teach how to grip a baseball at entry revel, they would say it should be like the photo bellow, but I want to cast a doubt on it. What I'm going to wright about in this article might be useful when you instruct little leaguers as their hands are smaller than adults' ones.
This grip, needless to say, is based on the common notion that throwing four-seam fastball is an essential basic skill for all baseball players. The notion partially stands on the fact that four-seam fastball is the least affected by the gravity force among all kinds of pitches thanks to the Magnus effect.
However, that is not the only reason why I don't recommend so-called four-seam grip. I have been doubting the validity of it because of its lack of mechanical stability. In the case of four-seam grip, as indicated in the photo below, the force from the index and middle finger can balance with the force from the thumb, but the force from the ring and little finger does not have its counterpart. So in this case, the ball is likely to slip out easily to the direction of vector 'a', and if you try to prevent the slipping out, you might throw the ball to the ground because of the strained grip.
So how should we grip the baseball alternatively? I recommend the way shown below. By shifting the thumb outside on the ball slightly, all the forces can get balanced. There are four points to keep the ball sustained in the hand, and those points make trapezoid.
This grip, needless to say, is based on the common notion that throwing four-seam fastball is an essential basic skill for all baseball players. The notion partially stands on the fact that four-seam fastball is the least affected by the gravity force among all kinds of pitches thanks to the Magnus effect.
So what pitches did they throw as their fastball? As you can see, the forearms of Pedro Martinez and Randy Johnson do not stand vertically at their release point, even though they had been throwing fastballs with considerably high velocity. They certainly used to use the so-called four-seam grip, but their each 'four-seam fastball' probably was not the backspin fastball. Such a case should be so common.
However, that is not the only reason why I don't recommend so-called four-seam grip. I have been doubting the validity of it because of its lack of mechanical stability. In the case of four-seam grip, as indicated in the photo below, the force from the index and middle finger can balance with the force from the thumb, but the force from the ring and little finger does not have its counterpart. So in this case, the ball is likely to slip out easily to the direction of vector 'a', and if you try to prevent the slipping out, you might throw the ball to the ground because of the strained grip.
So how should we grip the baseball alternatively? I recommend the way shown below. By shifting the thumb outside on the ball slightly, all the forces can get balanced. There are four points to keep the ball sustained in the hand, and those points make trapezoid.
Of course, shifting the thumb too much outside like the photo below is not proper because this makes the thumb touch the ball with its front face. Thumb must touch the ball with somewhat lateral face of it because if it touched the ball with its front face, you will come to grasp the ball too much strongly.
The way I recommend in this article would allow you to grip the ball more relaxedly and loosely because of its mechanical stability. And it is based on a premise that the back-spin fastball is not the only one correct answer for throwing fastball.