2026-09-05 · paper-digest
Lee & Ko: Human Umpires Shrank the Strike Zone by 17 Points With Two Strikes — Fukai Reads
An arXiv preprint by Kichang Lee and JeongGil Ko of Yonsei University. Using the Korean Baseball Organization's switch to automated ball-strike calling as an immovable ruler, they audit 1,216,246 pitches — restricted to those on the edge of the zone — to see how human umpires' calls moved with context. Called-strike probability was 17.17 percentage points lower in 0-2 counts and 6.61 points higher in 3-0 counts, and the pattern disappears under automation.
