Baseball players suffer from two types of fatigue: day-to-day (short-term) fatigue, and seasonal (long-term) fatigue.
Rested > Good > OK > Tired > Fatigued > Exhausted
Tired and Fatigued players will suffer gradually increasing performance penalties, and Exhausted players cannot play.
Each player has a current and maximum Endurance - when a player is fully rested these values will be the same, ex. 60/60. All players lose current Endurance points when playing; players with higher Endurance will fatigue proportionally more slowly than players with lower overall Endurance.
Example:
Player A: EN = 80/80 = 100% (fully rested)
Player B: EN = 40/40 = 100% (fully rested)
Both play a game and tire similar amounts
Player A: 78/80 = 97.5% rested
Player B: 38/40 = 95% rested
Pitchers lose fatigue points based on pitch count, at a rate of about one point of Endurance for every two pitches. So, a pitcher with a 50 Endurance can throw 100 pitches before being Exhausted and unable to pitch until he rests.
Each day off, a player recovers some of those "spent" Endurance points, and he'll be more rested. Generally any player will return to fully rested after threefour days of rest. However, other factors could influence this, notably Season Fatigue (see below).
There are a few ways keep your players rested, aside from manually adjusting lineups between games.
Season fatigue is the wear and tear a long season can have on a player. Season fatigue impacts playing in two ways:
You can not see season fatigue directly. However, if a player, when fully rested, never regains all his Endurance, you can bet that he's suffering from season fatigue in some degree
To offset season fatigue, rest a player more frequently. If a player never gets to the "Rested" status, you can be sure he's suffering from Season Fatigue. Sometimes, no matter how much you rest a player, they'll never be fully rested, especially if they're not as durable and have played a lot.
Note: Each game at DH causes less potential season fatigue than when playing a position. Toggle your use of designated hitters to extend low-endurance players.