The platoon factor batting adjustments are unclear to me. I have seen it explicitly stated that a left-handed batter receives a 4.5% bonus against a right-handed pitcher (and vice versa). How lefty/lefty and righty/righty matchups are handled is foggy.

Is it a bonus/no bonus differentiation, such that there's a 4.5% delta between the scenarios? Or is it a bonus/penalty differentiation, making it a 9% delta?

And how does this apply in the case of switch hitters?

(Apologies if this is well covered somewhere in docs, FAQ, or this forum; but I couldn't find anything definitive.)

its bonus/penalty, and for switch hitters there's no bonus or penalty

Thanks so much!

Does anybody know how this 4.5% manifests itself? Is it in any particular step of the decision tree, or is it in all of them? For example, does a hitter with platoon advantage have a 1.045x multiplier on their adjusted avg , or do they get that AND the 1.045x multiplier on bb rate, hr rate, etc ?

I have tried time and again to build a model that "stacks" platoon advantage, park, rest effects, etc and while my teams are generally good, it's hard to quantify if any of this is working. At the end of the day it's marginal effects that could be chalked up to random noise...but maybe there's something to it. A 1.045x multiplier on just hit rate would play differently than 1.045x multipliers on all of the above, in different parks.

From Paul Bessire's (former WIS guy) presentation in 2009, it appears to be only applied at the "hit or not a hit" stage:
https://image.slideserve.com/41801/pa-decision-tree-steps-2-n.jpg

Super helpful, thanks contrarian!

It's strictly applied to the "hit or not" as contrarian points out, and applied in the decision tree where that slide indicates. More specifically though, from later in the Paul Bessire slide show...

H/AB = ((1.066*AVG * .934*OAV) / LgAVG) /

((1.066*AVG * .934*OAV) / LgAVG + (1.066- 1.066*AVG )*(.934- .934*OAV)/(1-LgAvg))

Where, LgAVG = (.934*PLgAVG + 1.066*BLgAVG)/2

2000 Pedro vs. 1923 Ruth Example (with handedness):

H/AB = ((1.066*.393 * .167 * .934) / .2795) /

((.393 * .167) / .2795+ (1- .393)*(1- .167)/(1-.2795))

Where, LgAVG = (1.066*.283 + 0.934*.276)/2 or .2795

Result * Handedness = .2502 * 1.045

Final Result = .2614

The bonus (or penalty) is applied at the end, after all other pitcher vs. batter calculations are complete to determine hit or not.

It shows in a neutral matchup that '23 Ruth against 2000 Pedro would have a .2502 chance to get a hit or not.

With the platoon bonus applied that goes up to .2614

Very helpful. Two questions:
1. Is avg# going to align with the factoring of avg vs Blgavg (likewise oav# :: oav vs Plgavg)? That would make for a simpler calculation
2. Why is hitter avg given a 1.066x multiplier and pitcher oav .934x ? I can't think of a reason

For the second question, I think the hitter's ability has slightly more influence on the outcome of the plate appearance than the pitcher's ability, so it's weighted slightly toward the hitter's skill.

	HBP/PA	BB/(PA-HBP)	H/AB	K/(OUT)	HR/HIT	2B/HIT	3B/HIT
Pitcher%	47.8	43.5	46.7	45.6	39.7	15.2	11.6
Hitter%	52.2	56.5	53.3	54.4	60.3	84.8	88.4

That's a copy and paste job from the Bessire slideshow but it's clean enough to read. It's the weights applied to hitter and pitcher for each calculated event listed. The hitter's statistical contribution is weighted more heavily in every instance.