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 2026-06-12
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 Misiorowski, Jacob 111 1084 qualified
2 deGrom, Jacob 111 1142 qualified
3 Schlittler, Cam 110 1134 qualified
4 Skubal, Tarik 110 626 qualified
5 Rasmussen, Drew 109 897 qualified
6 Warren, Will 109 984 qualified
7 Nelson, Ryne 109 1016 qualified
8 Burns, Chase 109 990 qualified
9 Jax, Griffin 109 618 qualified
10 Ryan, Joe 109 1113 qualified
11 Kirby, George 109 1019 qualified
12 Junk, Janson 108 954 qualified
13 Ashcraft, Braxton 108 1057 qualified
14 Wheeler, Zack 108 664 qualified
15 Alcantara, Sandy 108 1340 qualified
16 Burke, Sean 108 1066 qualified
17 Woo, Bryan 107 1040 qualified
18 Chandler, Bubba 107 1028 qualified
19 Miles, Spencer 107 583 qualified
20 Perkins, Jack 107 520 qualified