Dickey is that he has as many as three distinct knuckleballs, though. Look at this plot of his knuckleball velocities from , and you start to see some clusters. Look at how many knuckleballs he throws above 80 mph.
And, as Dickey has evolved, those velocity clusters have changed. Check out Now the three clusters are more defined. Slow-mo at 74 mph, regular speed at 77 mph, and a fast knuckler around 79 mph. Of course, he still threw the odd super-slow-mo knucklers, but you can see where he settled in most days. You might notice something about the general graph in , though. It really looks like R.
A Dickey is throwing his knuckleball faster this year. Or, to say it more correctly, it looks like R. Dickey is favoring his fast knuckler more this year. And compare how often he throws a 74 mph knuckleball this year to how often he did so in He was especially successful in and He has made a slow start in A knuckleball is thrown at relatively low speed and with very little spin.
It is difficult to hit since the ball tends to change direction in flight as a result of the fluctuating aerodynamic side force on the ball. That force varies with the angle and location of the seam. The same thing happens with a rapidly spinning ball, but if the side force varies rapidly from positive to negative many times during the flight, the average effect is zero. With a knuckleball, the side force might vary in sign only once or twice on its way to the batter, with the result that the ball starts moving to say the left, then starts moving to the right and might then end up moving up or down, depending on the way the ball is spinning.
It is not easy to pitch a ball with no spin or even with very little spin. It is more natural to throw or pitch a ball by bringing the fingers down the back of the ball as it comes out of the hand, in which case the ball is thrown with backspin. Dickey grips the ball by digging his fingernails into the ball just behind the seam, and holding the ball between his thumb and third finger, something like in the attached drawing.
If he pushes forward as he releases the ball, so that the forces F1 and F2 are about equal, then there will be very little spin. Usually, a knuckleball rotates one to three times on its way to the batter, and the ball usually spins about an approximately vertical axis — that is, with side spin. Sometimes, the ball spins about a different axis, depending on which fingers push the hardest. To demonstrate that it is not all that difficult to pitch a knuckleball, this QuickTime video shows an example where I threw a knuckball and filmed it at fps.
The hard part is to throw it accurately, relatively fast and consistently well. Slow is, of course, relative when it comes to pitching. By comparison, fastballs in the majors average about 90 mph. Higher speeds mean less erratic movement, which helps him stay in the strike zone.
Whatever his secret, Dickey is flying high right now, along with his knuckleball. The views expressed are those of the author s and are not necessarily those of Scientific American.
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