Release Angles
Where each of a pitcher's pitch types leaves the hand, as horizontal and vertical release angle: one ellipse per pitch type, and how much they overlap. The more a pitcher's pitches share a release angle, the longer they look the same to the hitter.
Options
Overlap numbers
How it works
Release angles are the direction the ball is travelling as it leaves the hand: the pitch's trajectory is backed out from 50 feet to the release point (60.5 ft minus extension), and HRA and VRA are the horizontal and vertical angles that velocity makes with the line to the plate.
Each ellipse is a pitch type's 1-SD covariance ellipse of HRA against VRA. Pitch types with fewer than 20 pitches are left out. The frame is square, so a degree across is the same length as a degree up.
Overlap count shades each spot by how many ellipses cover it. Usage-weighted shades it by the share of the pitcher's pitches whose type covers it. Concentration splits the chart into segments — each exact set of overlapping ellipses — and shades each by how many pitches actually landed in it per square degree. Segments under 0.10 sq° stay on the map but are left out of its scale.
Play loop cross-fades through the four. Share image copies or downloads the view shown as a 2320 × 2320 still. Its menu also downloads the loop as a GIF (1080 × 1080 at a steady 20 fps, sized for X (Twitter)), or the four stills and the loop as one zip.
Data: MLB's StatsAPI trajectory fits, from this site's nightly pitch-level data files. A port of release_angles.py.