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 2026-09-26
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 112 774 qualified
3 Montgomery, Mason 110 643 qualified
4 Skubal, Tarik 110 1369 qualified
5 Misiorowski, Jacob 110 1786 qualified
6 deGrom, Jacob 110 1908 qualified
7 Taylor, Grant 109 836 qualified
8 Schlittler, Cam 109 1701 qualified
9 Scott, Tanner 109 576 qualified
10 Jax, Griffin 109 1062 qualified
11 Nelson, Ryne 109 1139 qualified
12 Rodriguez, Bradgley 109 678 qualified
13 Burns, Chase 109 1802 qualified
14 Rasmussen, Drew 108 1743 qualified
15 Loáisiga, Jonathan 108 609 qualified
16 Petersen, Michael 108 621 qualified
17 Ashcraft, Braxton 108 1457 qualified
18 Smith, Cade 108 781 qualified
19 Chapman, Aroldis 108 542 qualified
20 Miles, Spencer 108 1015 qualified