Kagan: The physics of the gyro pitch

From SABR member David Kagan at The Hardball Times on December 1, 2017:

We need to have a heart-to-heart about the flight of pitches and the spin of the ball. You already know the spin on the ball induces the air around the ball to exert a Magnus force on the ball. That is, a ball with backspin feels an upward Magnus force keeping the ball from falling as fast as gravity requires, while topspin does the opposite. Sidespin results in a pitch veering left or right depending on which way the ball spins.

Here’s the problem with that thinking. The topspin, backspin, and sidespin are all measured with respected to the velocity vector (direction of motion of the ball). The trouble is, the direction of motion of a pitch is changing on its journey from the mound to the plate. So, the direction of motion is changing.

So, the question is, does the spin stay oriented with respect to the motion of the ball as it drops or veers to the side or does the spin stay fixed with respect to the field? So that you really understand what I’m getting at here, let’s think about gyrospin instead of topspin or sidespin.