Found it under Player Settings > HELP > Auto Rest explanation;
- This value is associated with the player's fatigue level as he enters a game. The fatigue level is under the % on this page. If a player's % is below his Auto Rest value on game day, he will automatically be removed from the lineup and will not play in the game. If it's a position player, he must have a backup listed in the Player Rest hierarchy or else he'll remain in the lineup. Based on the status of the team (other players' fatigue), there are occasional instances where a player will play despite being under his auto rest setting. To edit this value, please click on the dropdown arrow for the player under player rest and select one of the values listed. You may choose not to use this feature for the player by selecting N/A (not applicable). In this case, the player will be available to play in every game no matter how low his stamina is. Pre-game fatigue effects the player's maximum performance for the game. As the player is used throughout the game, he may fatigue more and incur a larger performance hit. On top of the performance hits, fatigued players are also more prone to injury.
The player entering the game for replacement will be chosen based on your rest hierarchy as indicated under the Manager Settings tab. Please note, you can adjust the default auto rest setting from the Management Console.
This kind of explains my division rival Monterey. They were 58-33 before all star break then 37-30 after. It was the same thing last year. He never rests his guys and they are all hovering about 90-92 fatigue for playoffs;
You can take a look at his current fatigue in the box score.
This also shows me when pitchers are kept in longer, and are pitching at 10-20 fatigue, they are more apt to give up runs and thus you should adjust your Call Bullpen stat appropiately. But it also makes me think Why not get 4-5 starting pitchers for relief, because your relief will never be low fatigue. They will always be coming out at 50-70. Might be a strategy to try out of course starters are expensive.
This also puts a big emphasis on the by week. All of my players will be 100 in the next bracket while the lower seeds will be a bit winded. Pretty huge.