if the pitches behave in the same way as they did previously, it's most definitely not fatigue. if a cutter doesn't cut as much, then it's clearly part of the phenomenom of study. this would be the simplest way to rule this out or show that it is defintely a possible cause due to it's change in behaviour.
there must be a cause for change! if behaviour remains the same, it is not the impetus of that change in result!
the phenomenom is an end result... it's no doubt a culmination of multiple things working together. however, the weights of those things are what people are arguing about. don't get me wrong, i like arguing too
you simply map out all of the forces invovled and see what the data says... you don't pick cherry pick 1 thing and say that is a good answer, like that baseball prospectus link did.
this guy is a psycologist.. .his stats class was some dumbed-down "stats for the life sciences" BS... it's like "calculus for the life sciences" that M.D.'s take... it's stupid-calc and stupid-stats. i know, i took theh calc one and a real calc class, lol. you learn the same concepts but in a less sophisticated way/less depth. just enough to be able to understand the results of various white papers/research.
he picked a path instead of letting the path present itself... you will easily find false-positives doing things this way. he found an answer he wanted to find. you can't go into it "wanting" somethign ... most people cannot be impartial in that light.
if you want to take a mass amount of data and make it say somethign specifically, you can do so... even when that statment is likely wrong. and all the math can be perfectly done and logical... but the overall approach is the fault.