I’ve been thinking about this ever since I saw a picture of a local kid throwing a baseball where I thought the seams looked weird. I have a digital copy of the pic, if it’s possible somehow to share it here, let me know.
The gist was that it looked like a two seamer going sideways.
I thought it looked familiar, and I found the exact same depiction of a baseball rotation in the book The Physics of Baseball.
In that book, a slider is described as the white part of the ball being the dot as opposed to the seams. Some might say that if you see the red dot, what you’re really looking at is the spin described in the gyro ball articles as rifling spin, or the same spin that a football spiral would have.
So what this kid’s newspaper pic ball looked like was the slider described in the book only spinning in the opposite direction.
I later went out to a game and caught this pitch on video…
I think what is going on is that this pitch was a two seam fastball only released somewhat laterally so that the backspin is now on it’s side. The ball is thrown right down the middle, but backs away from the opposite hand hitter.
The movement is a little like a screwball.
Bottom line is that this lateral rotation is what the Physics of Baseball calls a slider. Since the rotation on this ball is in the opposite direction of the P.O.B.s slider illustration, I called it the back up slider.