What's the accepted theory on in-game pitcher fatigue - do pitchers get less effective during the game as they rack up pitches?  I know if a guy hits 100% and pitches the same day, he will end up a lot more fatigued than if he had one more day of rest at 100% and threw the same number of pitches.

Yes, as a pitcher goes on he gets marginally less effective, generally. Though I reject the second half of your post; I never give guys an extra day of rest anymore and find it makes them no more fatigued than pitchers got when I used to give them an extra day.

Absolutely, the second part of his post is true.    That can be very easily tracked and observed.

It becomes more noticeable towards the end of the season.

I'll disagree with that.  Pitching fatigue is pretty constant and predictable throughout the season.  It's not a cumulative, season-long phenomenon as is position player fatigue.

admin has mentioned that pitchers have a "pool" of innings, and once it's used up, they fatigue much faster.

Do you have a reference point for that statement?  Dev chat, ticket, anything?  Because I don't recall ever seeing that.

I know that SLB works that way, but the HBD pitching fatigue is based on a different model.

All I could find was actually an answer to a question you asked, but it's hardly concrete.  The last part of his answer..."It is for season fatigue, of course."  I may keep digging later tonight.

HBD - 2/11/2009 11:00:00 AMView Chat

I have a two-part question about pitching fatigue: (1) is there such a thing in HBD as "in-game fatigue", in which a pitcher may start to tire and become less effective the deeper he pitches into the game; and (2) if there is, with all else being equal, would a pitcher who was "75 (100)" on the day before his start be more likely to experience in-game fatigue earlier in the game than would a similar pitcher who was "100 (100)" for one or more days before his start? (tecwrg - Hall of Famer - 1:30 PM)

Yes and no. It's all about the pitcher's fatigue at the start of the game, recent wear is not part of the in-game fatigue. It is for season fatigue, of course.

In my experience, both of you are right.  And wrong.

Here's what I've observed(and mhul isn't making that up.  I've seen it also):
Using pitchers one the first day at 100% won't matter initially.   But, as the season progresses, they fatigue more rapidly/recover slower.   I've used a high dur ace as soon as he was 100% to try to maximize his innings.   Everyone else was getting the extra day.  It didn't take long before he was taking his regular spot in the rotation instead of being bumped up a day here and there.

Thanks - so... there is an in-game fatigue model but it is not connected at all to the day by day recovery model.  I would think those being coupled would have made a lot of sense, but at the moment I just need the answer.  Is that the correct takeaway from the post here?  I know I'm sounding dense, but am in the middle of a WS and have pitching decisions to make.

It's virtually impossible to say if performance and recovery are connected.    I would say "Yes".    If I have two identical pitchers and one throws 100 pitche and drops to 42% and the other throws 100 pitches and drops to 22%, I have to believe the guy at 22% threw more less effective pitches if I believe in-game fatigue exists.

Yeah - that was the whole reason for the post, but the dev chat said it pretty outright for them - on a lot of these questions you get half an answer at best to keep the engine more mysterious.