BF fatigue/rest methodology

The new batters faced (BF) fatigue/rest ratings are based on actual MLB pitcher usage.  Here’s a breakdown of the methodology used to generate the ratings.

Fatigue

All pitchers receive a RP fatigue rating, but a pitcher must have at least one MLB start in order to receive a SP fatigue rating.  In general, the fatigue rating is the highest of:

1. 80% of the highest number of batters faced (BF) in a single appearance
2. 90% of the second highest number of BF in a single appearance
3. 90th percentile ordinal rank of BF values from all appearances (max: 4th highest ordinal value)

Pitchers who started at least 50% of their appearances receive a RP BF rating no less than 2/3 of their SP BF rating.  Also, pitchers are not allowed to have a SP rating that is less than their RP rating.

example, Justin Verlander as a SP (BF per start):

verlj001, 35, 34, 33, 32, 31, 30, 30, 30, 29, 29, 29, 29, 29, 28, 28, 28, 27, 27, 27, 26, 26, 26, 26, 26, 26, 25, 25, 24, 24, 24, 23, 21, 16

1) 80% of highest (35) = 28
2) 90% of 2nd highest (34) = 30
3) 34 starts, 4th highest ordinal value (32) = 32

Verlander SP fatigue = 32

Rest

Rest ratings are based on BF totals after appearing in a relief role.  BF are cumulative over consecutive days pitched.

The BF cutoff for zero days rest is simply the highest number of BF accumulated while pitching over consecutive days.  A pitcher must have pitched at least once on back-to-back days in order to receive a zero day rating.

The BF cutoff for 1 day rest is the highest of the following:

1. longest BF stint prior to 1 day off
2. 0-day cutoff + 50% average BF for all appearances on 0/1 day rest
3. 25% of longest overall BF stint

The BF cutoff for 2 days rest is the highest of the following:

1. longest BF stint prior to 2 days off
2. 1-day cutoff + 50% average bfp for all 0/1/2 day appearances
3. 40% of longest overall BF stint

The BF cutoff for 3 days rest is the highest of the following:

1. longest BF stint prior to 3 days off (max 21)
2. 2-day cutoff + 2
3. 50% of longest overall BF stint