[QuantaCondor]

Amazing, ridiculously detailed post. This should be standard reading (if not stickied) for anyone looking to dive deeper into how PT works.

I'll add a few general comments that I think are worth saying, just as a supplement from another PT modelmaker's point of view. Overall, many assumptions stated here and more broadly in older posts in the community are about how the PT21 engine works (and in some cases, about earlier games). There's no guarantee that one single thing stays the same from year to year. That's why the most important takeaway here is the overall strategy for gathering data and analyzing it, rather than any specific assumption. This is especially true for statements like "this particular stat is important" or "the breakpoints are here".

For example, avoidK wasn't nearly as important in PT20. Control wasn't nearly as strongly scaled in PT20. OF defense was much worse in PT21 vs PT20, and 2B defense was much better. Catcher defense changed radically. And when you switch out the eras or metas for something else, something which I anticipate will be relevant in PT22, you need to basically re-evaluate many of your scale factors and assumptions to see what holds and what changes. Even just within the same game, moving from base game to standard tournaments changes how you have to view players by a lot. The best players know how the different environments affect their assumptions, which is an intuition you develop by analyzing these different environments and seeing what changes and what stays the same.

Another general point I'll make is that I have found weighing your regressions by PA and IP make a ton of difference in terms of how much data you need to assess a particular environment. Some stats need more data, like HR%, but things that happen more frequently like BB%, K%, and even BABIP scaling converge much more quickly. This is useful especially in things like perfect or certain tournament formats where you don't have the luxury of many weeks of data and/or the format meta shifts quickly and you want to be proactive about solving it.

The last thing I'll mention is that the most important feature of a good OOTP model is validation. You can slam whatever coefficients into your spreadsheet or script you want, but comparing the projections to what you actually see (including at extremes!) is frequently where you learn the most about the game. It's also enlightening to compare your analysis to that of other players, to test your assumptions, and constantly question if what you're doing is really the best way to do it.

Again, awesome post by scipper here. Many of the comments are true regardless of the PT version you're on, so hopefully it can be one of those posts people link to even beyond PT22.