From another post
1) NERP defense adjuster for pitchers
The worst fielder among pitchers avaiable in ATG is Frank Bertainia. His fielding rating is 5e51. The NERP value of his defense is +1.09. On the opposite hand, the Glavines of ATG world (1e0) have a NERP fielding value of -0.17. Everything else is in between.
To put that in a formula is kinda complicated, because some errors are added to hits, but if you want it, here it is
A) 2*(ROUNDUP(1.5*(range-1);0)/20)+errors/54*2*ROUNDUP(1.5*(range-1);0)/20+errors/54*2*(20-(roundup(1.5*(range-1);0)))/20.
B) Anything in excess of 2 of this sum must be put in another column.
C)Then you take the sum (in A) X 0.56 + the excess (in B) X 0.31 minus 0.17.
BK and WP have a slightly greater range. The worse ratings are found in Dave Stewart and Ontiverious (curiously, both Oakland As members of the 1988) with balks and wp at 17 apiece. The net NERP adjustment is + 2.09 for these two pitchers. You have to consider though that WP happen twice as frequently than BK, so for example David Cone's 1988 card (BK=17 WP=9) has roughly the same NERP adjustment on this regard compared to Nolan Ryan's 1986 card (BK=0; WP=17)--both at 1.4. 1990's Dave Stewart (BK=0, WP=6) has a NERP adjustment of 0.5. In fact, these are roughly estimates...in theory you should adjust these ratings for the on-base presence (a pitcher with a WP of 8 will allow more wild pitches than a pitcher with a WP of 6 that allows half the on-base).
Holding too is affected by the level of on-base, so in theory it too should be influenced by how much on-base a pitcher will allow. I'm less on solid grounds on how to adjust NERP for holds in ATG, but my rule of thumb is to adjust the NERP by adding +1 for the very bad holders (+5 and above) and by substracting -0.15 to the best holders (-6):
+5 and above +1
+4....0.92
+3....0.83
+2....0.66
+1...0.51
0...0.38
-1...0.26
-2...0.15
-3...0.07
-4...0
-5...-0.1
-6...-0.15
What this post doesn't say is that the NERP adjustments described above (eg. +/- 2NERP) are based on 216 PA. So you have to multiply any value you get based on 216 PA for the course of a full season.
The NERP value for say for one BK and one WP is 0.29.
For recall, the NERP formula is roughly the same as: 0.47*1B +0.78*2B + 1.09*3B + 1.42*HR + 0.33*(WALK+HBP).
I also make a further adjustment to account for the fact that cards are based on plate appearences (be it 108 PA for one card only or 216 PAs when considering both offense and defense) whereas our REAL interest in valueing pitching is based on outs.
In other words, what we are REALLY interested is in how much my pitching will give before I get 27 outs----and NOT how much my pitch will give before my opponent reach its 27th plate appearences.
The net result when you go from NERP based on PA to NERP based on outs is that pitchers who allow a lot of on-base are penalized somewhat.