Skill Changes, September 23

16 of 153 pitchers with a real velocity change, 8 of 437 more whose stuff or command has moved, 8 of 144 hitters with a measurable skill shift.

The inputs, not the results. A pitcher who has lost velocity is a different pitcher before his ERA catches up, and a hitter whose contact quality has shifted is a different hitter before his batting average agrees.

Pitchers losing velocity

Year-over-year on the primary fastball, for pitchers with at least 100 of them in both seasons. Velocity is the earliest and least ambiguous signal an arm gives you: it moves for physical reasons and it stabilises faster than any result stat. A full mile per hour is roughly the tenth percentile of the league, real, not drift.

Pitchers gaining velocity

The same measure the other way. Added velocity on a starter often means a mechanical change or a role change; on a reliever it is usually the shorter outings doing the work.

Pitchers changing stuff and command

Stuff+, Location+ and Pitching+ measure the pitch itself rather than what the hitter did with it, so they move before the ERA and before the strikeout rate. This is a slower read than velocity and a broader one: it catches a new slider or a command gain that the radar gun never sees. Ordered by the size of the change, then by where the arm sits on our board.

Hitters

Contact quality and swing decisions, the parts of a hitting line that settle before the results do.

How to read this

Velocity is the most trustworthy line here. It stabilises quickly, it moves for physical reasons, and a starter who has genuinely lost a mile per hour is usually telling you something before the ERA does. It is measured on the primary fastball only, and only for arms with a real sample in both seasons.

The stuff and command section is a descriptive layer and is not part of our projection, and neither is the hitter section. Neither has been validated into the rankings and we do not pretend otherwise: where these and the board disagree, that is something to watch rather than a correction to either.

Low-confidence signals are excluded from both sections, a little under half the feed. A small reading off a handful of batted balls or a few dozen pitches is noise wearing a decimal point.

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