Grip Lab

Read the hand’s bias from the fastball, then pick grips that use it.

Fastball inputs

% (0.96 also works)
rpm
mph · optional, enables Bauer units
Movement-inferred · clock or Trackman degrees
Spin-based (observed) · same format
inches · for arm angle
ft
ft from center · sign ignored
● marks the inputs that drive the bias score.
° · zone-average fastball
° · + = toward arm side
Example athlete

Bias read

—
◀ SupinatorNeutralPronator ▶
Measured tilt Spin axis (movement) Expected from slot
SignalValueLean
Pitcher's viewRight hand
Drag to orbit · scroll or pinch to zoom
Fastball

Four-seam

Tilt—
Spin eff.—
Spin—
Seams—
Ranked for this athlete

Grip recommendations

Match % = bias fit + seam, spin and approach-angle rules
How the bias score works

Every angle is converted to an arm-side angle measured from 12:00 in the pitcher's view, so RHP and LHP read the same way. Each signal becomes a lean from −1 (supinator) to +1 (pronator), then a weighted sum gives the score from −100 to +100. Missing inputs drop out and the remaining weights rescale.

  • Spin efficiency (28%). Pronated fastballs tend to be efficient; supinated ones pick up gyro and cut. Centered at 85%, full lean at ±12 points.
  • Seam-shifted wake (24%). Spin axis minus measured tilt. Movement that runs more to the arm side than the spin predicts reads pronator; movement that cuts or carries against the spin reads supinator. Full lean at ±25°.
  • Tilt vs. arm slot (20%). Arm angle comes from release height minus 70% of standing height, over release side. Expected fastball tilt is 90° − arm angle − 10°. A tilt deeper to the arm side than expected reads pronator.
  • Spin rate (16%). Bauer units (rpm ÷ mph) when velocity is entered, otherwise raw rpm. High spin leans supinator.
  • VAA (12%). Adjusted for release height. A flatter fastball than the release height predicts usually means carry, which leans supinator. HAA is used only in the grip rules, because it depends mostly on location.

Below ±20 the athlete reads neutral; past ±55 the lean is strong. These cut points and weights are starting calibrations. Check them against your own athletes before you rely on them.

3D hand model credit

Hand model: "generic-hand" from WebXR Input Profiles (github.com/immersive-web/webxr-input-profiles), used under the MIT License.

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