We call the spin that contributes to movement as Active Spin
. When thrown with pure top or backspin, then 100% of the spin contributes to movement. You can also throw a pitch with some side-action so that some of the deflection will go up or down, and some will go side to side. All of this is Active Spin.
For a football, none of the spin contributes to movement, and so, a football has 100% Gyro Spin. In order for a baseball to have Gyro Spin, you would twist your arm slightly so that the baseball is thrown more like a football. The more the baseball is thrown like a football, the more the spin of a baseball will go from Active Spin to Gyro Spin.
We provide active-spin data derived from two methods. In both cases, we isolate the spin in the active plane and compare it to the total amount of spin. The recommended method is the directly-measured active spin, and this corresponds to the Active Spin % found on the Spin Direction
Measured active spin uses the 3D spin vector at release; this is only possible with the 2020 season going forward. (Label is "2020 - Spin-based" and can be read as "Active Spin using the Spin-based method".)
Inferred active spin from movement uses the total amount of movement to estimate the amount of active spin, if we presumed only magnus was at play; this is a legacy method that can be useful in certain circumstances. (Label is "2020 - Observed" and can be read as "Active Spin using the Total Observed Movement method".)