K% and BB% — Per-Plate-Appearance Rates

K% = strikeouts / plate appearances; BB% = walks / PA. K/9 and BB/9, by contrast, are per-9-innings and depend on opponent batting average.

K% is the cleaner measure of dominance because pitchers with low opponent batting averages have inflated K/9 numbers (fewer batters per inning).

Modern MLB benchmarks: K% 22% = league average, 25% = above average, 30%+ = ace, 35%+ = historic. BB% under 6% is excellent; 10%+ signals control problems.

K-BB% (the simple difference) is a beloved single-number summary of pitcher quality. 20%+ is Cy Young territory — Roki Sasaki and Yoshinobu Yamamoto target this band.

→ Related: K/9 & BB/9 / FIP / Stuff+