K/9

Strikeouts per nine innings — a pitcher's swing-and-miss rate. Higher means more bats missed (less reliance on defense and luck); ~9+ is high-strikeout. A jump or drop in recent K/9 often flags a change in stuff or health.

• ERA — Earned runs allowed per 9 innings. Lower is better; under ~3.50 is strong.
• WHIP — Walks + hits allowed per inning. Under ~1.10 is excellent, over ~1.40 is shaky.