Probably more about the pitch count than anything but they would also have a fatigue model that uses all of this info:
Pitch count
Inning count
Pitches per inning
Number of up-downs
Maybe other stuff like weather, pitch types being thrown, favourite mario kart character, sexual preference, what he had for breakfast, girth, and so forth
There is science based on their fatigue unit regression models, and that is distilled to the stupid coaches and is probably something like: 70 P max, and 3 up-downs max, and never 35+ P in one inning