Mithrandir Metrics
Mithrandir+ / v1.1.c / production

Mithrandir Stuff+ pitch quality index.

A 100-anchored pitcher stuff index trained on Statcast pitch-event run value.

Y-Y r²
0.504
Stabilization
100 pitches
RMSE vs FIP
-0.168
Version v1.1.c Status production Snapshot 2026-10-25
Definition / formula

2020-2023 Statcast pitch-event backfill via pybaseball; validation 2024; held-out 2025.

Stuff+ = 100 + z(predicted pitch run prevention) * 10
Method note

v1.1.c uses the methodologically correct delta_run_exp target and original feature set after ablation.

Method note

Spin axis, stand, and platoon additions were tested and dropped because they added noise.

Validation / what it does not measure
Y-Y r² 0.504 Stabilization 100 pitches RMSE vs FIP -0.168
Does not measure

It does not fully capture command, sequencing, scouting reports, or hitter-specific exploitation.

Does not measure

Per-pitch-type Arsenal Decomposition is descriptive support under Stuff+, not a separate promoted predictive metric.

Top 20 / current cached snapshot
Rank Player Metric Sample Status
1 Megill, Trevor 112 587 qualified
2 Morejon, Adrian 112 790 qualified
3 Montgomery, Mason 110 677 qualified
4 Skubal, Tarik 110 1369 qualified
5 Misiorowski, Jacob 110 1854 qualified
6 deGrom, Jacob 110 1908 qualified
7 Taylor, Grant 109 836 qualified
8 Scott, Tanner 109 590 qualified
9 Schlittler, Cam 109 1701 qualified
10 Nelson, Ryne 109 1161 qualified
11 Jax, Griffin 109 1114 qualified
12 Loáisiga, Jonathan 109 633 qualified
13 Burns, Chase 109 1802 qualified
14 Petersen, Michael 109 647 qualified
15 Rasmussen, Drew 108 1743 qualified
16 Rodriguez, Bradgley 108 712 qualified
17 Smith, Cade 108 786 qualified
18 Ashcraft, Braxton 108 1457 qualified
19 Chapman, Aroldis 108 542 qualified
20 Kelly, Kevin 108 637 qualified