Outfield Arm Rating Scale - Quick Reference

Normal Distribution (-6 to +5)

                     NORMAL DISTRIBUTION CURVE

    Elite                                              Very Weak
    -6                          0                          +5
    |                           |                           |
    |  -5  -4  -3  -2  -1   |   0   |   +1  +2  +3  +4  +5 |
    |                       |       |                       |
    |<--- Above Average --->|Average|<--- Below Average --->|
    |      (Top 50%)        |       |     (Bottom 50%)      |

    0.6% 2.3% 6.7% 16% 31% 50% | 50% 31% 16% 6.7% 2.3% 0.6%
         Players at each percentile

Rating Breakdown

Elite Arms (Negative Ratings = Better)

Rating	Description	Z-Score	Approx %	Frequency
-6	Elite Cannon	> 2.5	~1%	Very Rare
-5	Outstanding	2.0-2.5	~2%	Rare
-4	Excellent	1.5-2.0	~3%	Uncommon
-3	Very Good	1.0-1.5	~5%	Above Avg
-2	Above Average	0.5-1.0	~15%	Common
-1	Slightly Above	0.0-0.5	~30%	Common

Average Arms

Rating	Description	Z-Score	Approx %	Frequency
0	Average	-0.5-0.0	~40%	Very Common

Weak Arms (Positive Ratings = Worse)

Rating	Description	Z-Score	Approx %	Frequency
+1	Slightly Below	-0.8--0.5	~20%	Common
+2	Below Average	-1.2--0.8	~10%	Above Avg
+3	Poor	-1.5--1.2	~5%	Uncommon
+4	Very Poor	-1.8--1.5	~2%	Rare
+5	Very Weak	< -1.8	~1%	Very Rare

Note: Thresholds calibrated to actual data after 300x assist_rate weight compressed z-score distribution.

Expected Distribution (162 Players)

Based on normal distribution, in a typical season with ~162 qualified outfielders:

Rating Range	Count	Description
-6 to -4	~10	Elite/Excellent arms (top tier)
-3 to -1	~62	Above average to very good
0	~18	Average (largest single group)
+1 to +3	~62	Below average to poor
+4 to +5	~10	Very poor/weak arms (bottom tier)

Comparison to Previous Scale

Old Scale: -6 to +2 (9 levels)

Skewed toward negative (better arms)
Limited granularity for weak arms (only 3 levels: 0, +1, +2)
Not symmetric

New Scale: -6 to +5 (12 levels)

Symmetric distribution around 0 (average)
Equal granularity for elite and weak arms
Follows normal distribution percentiles
More meaningful differentiation at extremes

Practical Guidelines

For Elite Arms (-4 to -6)

Strong deterrent effect on baserunners
Frequently throw out runners attempting to advance
High home plate assist count
Can turn singles into outs on aggressive baserunning

For Average Arms (-1 to +1)

Typical MLB outfielder arm strength
Will get assists but not at elite rate
Runners will test them opportunistically
Positioning and reads matter more than raw strength

For Weak Arms (+3 to +5)

Runners take extra bases frequently
Low assist totals relative to opportunities
May be limited defensively to certain positions
Often DHs or older players playing outfield occasionally

Integration Notes

When implementing, ensure:

Minimum 50 balls fielded for qualification
Position-specific baselines (LF/CF/RF different)
Z-score calculation accounts for position
Players below sample size get 0 (average) rating

Reference: /docs/of_arm_rating_improvement_proposal.md for full methodology

3.9 KiB Raw Blame History