How does SDS determine which pitches a pitcher has in his repitoire?

Take LS Rich Hill for example.

Beginning of last year he had three pitches. I think the were a fastball a 2 seam fastball and a curve.

Then towards the end of the year they added a 12-6 curve, I think, that gave him three pitches.

Now for 21 he has 5 pitches. A 4 seam fastball, a sweeping curve, a slider, a cutter, and a 2 seam fastball.

Do they just throw darts at a borax of pitches and whatever sticks they assign?

Seriously though, how do they determine what pitches a pitcher has in his repitoire?

Based on which pitches they threw last year, I think.

Pretty sure they use baseball savant... Which shows pitch arsenal and usage

@nanthrax_1_psn said in How does SDS determine which pitches a pitcher has in his repitoire?:

Pretty sure they use baseball savant... Which shows pitch arsenal and usage

I think Ramone may have even said just that in the last stream.

Baseballsavant lists Rich Hill's 2020 repertoire in order of frequency as fastball, curveball, cutter, slider, and sinker. In 2019 Hill threw a fastball, curveball and slider above a 2% rate.