Bruce Bundy has developed formulas over the year that predict a pitcher's card with 95% accuracy or so. You have the formulas below. The full explanations are found on his website:
http://www.cba-bb.net/Bundy.htmTo answer your question, there is no one single stat that you could rely with full accuracy.If I were to pick one, it would be pitcher's opponent OPS, but still, you would need to make adjustments to have a better idea of what the pitchers's card would look like, adjustments for leagues (National vs American), for stadium environment, and for team's defense. Stadium environment is based on a 3-year period, so this year's stadium rating are probably a good indicator of how you should adjust HR allowed for this year pitcher's card. Ideally, you should also take away HBP and Intentional walks out of OPS, since SOM does not consider the latter two when making the pitcher's card.
You could probably skipped the non-intentional walks for starting pitchers without too much impact, but relievers are more affected by this stat. Seung Hwan Oh this year allowed 13 walks while facing 250 hitters, which is a pretty good ratio. But 8 of the those 13 walks were intentional. So he really allowed only 5 walks, which is outstanding. His card won't have any walk on it (a pitcher must allow more than 9 walks per 108 hitters faced to have walks on their cards).
But you could try Bundy's formula and try to make your own estimates.
In short, non-IBB, doubles, and triples seem to be only affected by league's adjustment.
Home runs are adjusted by the environment of the pitcher's team. Singles too, and they are further adjusted by the quality of the pitcher's team's defense.
In bold italic are constats you should adjust per league, by roughly a 4% difference (consider 8.8 for NL and 9.2 for AL instead of taking 9 in formula #16.
FORMULA #15: PITCHER'S TBF
pTBF = ( IP * 2.95 ) + HITS + ( W - IW )
FORMULA #16: PITCHER'S WALK
sompW = (( W - IW ) * 216 ) / ( TBF - IW )) -
9 FORMULA #17a: PITCHER'S HIT
sompH = ((( HIT / TBF ) * 216 ) - 29.4 ) + XF
(XF = Xchart FACTOR; DEFAULT = 4.9)
FORMULA #17b: PITCHER'S HIT
sompH = ((( HIT * ( 168 - sompW ) / (( TBF - IW ) * .265)) + (((( 2 * oppBA ) - .
265 ) * 30 ) - XF)
FORMULA #18: PITCHER'S DOUBLE
sompD = (( D * 216 ) / (TBF - IW )) -
90 FORMULA #19: PITCHER'S TRIPLE
sompT = (( T * 216 ) / (TBF - IW )) -
15 PRE 1990 FORMULA #19
sompT = sompHR * .4
FORMULA #20: PITCHER'S HOMERUN
sompHR = (( HR * 216 ) / (TBF - IW)) -
50 FORMULA #21: PITCHER'S STRIKEOUT
sompK = (( K * 216 ) / ( TBF - IW ))
FORMULA #22: PITCHER'S HOLD
sompHOLD = (( SB / ( SB + CS )) - .6666 ) * 20
FORMULA #23: PITCHER'S POINT OF WEAKNESS
sompPOW = IP / APP
FORMULA #24: PITCHER'S ERROR
sompERROR = ( E * 1458 ) / IP
FORMULA #25: PITCHER'S BALK
sompBALK = ( BALK * 290 ) / IP
FORMULA #26: PITCHER'S WILDPITCH
sompWILDPITCH = ( WP * 200 ) / IP
FORMULA #27: PITCHER'S CLOSER RATINGS
sompCLOSE =0=N; 1-3=0; 4-6=1; 7-9=2; 10-14=3; 15-19=4; 20-29=5; >30=6
FORMULAS #28:W POWER HR ADJUSTMENT
somHR = ((
(leagueHR/leaguePA)*20)*(108-somHBP-somW))+somHR(under 10)