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 2026-07-26
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 Morejon, Adrian 113 545 qualified
2 Taylor, Grant 111 522 qualified
3 Misiorowski, Jacob 111 1191 qualified
4 deGrom, Jacob 110 1329 qualified
5 Skubal, Tarik 110 798 qualified
6 Schlittler, Cam 110 1219 qualified
7 Nelson, Ryne 109 1111 qualified
8 Burns, Chase 109 1090 qualified
9 Jax, Griffin 109 777 qualified
10 Rasmussen, Drew 109 987 qualified
11 Ryan, Joe 108 1399 qualified
12 Warren, Will 108 1243 qualified
13 Ashcraft, Braxton 108 1143 qualified
14 Kirby, George 108 1019 qualified
15 Smith, Cade 108 533 qualified
16 Woo, Bryan 108 1321 qualified
17 Junk, Janson 108 954 qualified
18 Burke, Sean 108 1154 qualified
19 Chandler, Bubba 108 1125 qualified
20 Alcantara, Sandy 107 1340 qualified