There are two major issues with current pitch tracking in the MLB.
- The measurement system, Trackman, does not make a direct measurement of the spin that contributes to Magnus force.
- It assumes all accelerations are constant over the entire flight of the ball.
Each of these is important. I know the Hawkeye system that will replace Trackman next year will eliminate (1). But, most non-MLB folks will still be using Trackman or Rapsodo and will still have this issue.
The constant acceleration assumption seems like a way to reduce the amount of data that needs to be recorded and perhaps a way to smooth noisy data. I have no idea whether or not Hawkeye will solve (2). At minimum, it would be nice if acceleration could be a bit more nuanced than constant. Maybe linear or even a polynomial. It is unknown to me if the Trackman (or future Hawkeye) data are sufficiently resolved in time and space to support this.
One other thing I’d like to point out is that the impact of (1) is different with Trackman than it is with Rapsodo. In fact, Rapsodo 1.0 and 2.0, which measure the ball’s rotation at different points in the flight, are impacted differently. They all work great if the ball isn’t experiencing a non-Magnus force.
If you want to find out what your Trackman or Rapsodo will make of a Seam-Shifted Wake pitch, just scuff a ball on its pole and see what it says. It can’t read that. An example is shown below. This is Rapsodo 1.0
The ball is scuffed significantly on the right side. Note that while the ball broke left about two feet (0 would be about the vertical pole on the L screen), Rapsodo says -1 inch. That’s because it correctly got the tilt near 12:00 and that axis gives 0 horizontal break from Magnus. Note that Rapsodo 1.0 accurately tells you the pitch location independent of these issues.