Baseball players generally suffer from two types of fatigue: day-to-day (short-term) fatigue, and the seasonal (long-term) fatigue.
Fatigue is a factor of a player's Endurance. 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 a similar number of Endurance points when playing, but a player with higher overall Endurance will fatigue proportionally more slowly than players with lower overall Endurance.
Player A: EN = 80/80 Fatigue = 100%
Player B: EN = 40/40 Fatigue = 100%
Both play a game and tire similar amounts
Player A: 78/80 = 97.5% rested
Player B: 38/40 = 95% rested
As you can see, both players suffered the same endurance loss, but because Player A has a greater overall Endurance rating, the effective fatigue he suffers is less than the less-durable Player B.
Pitchers lose fatigue points based on pitch count. Whereas players lose a little fatigue each day, pitchers may lose a lot of fatigue on any given day (especially starters). As a result, pitchers need more rest to get back to 100%.
Each day off, a player recovers 1/3 of his maximum Endurance. So, a player with an Endurance of 60 would recover about 20 points of Endurance after a day off. As a result, any player - pitcher or position player – will generally return to their maximum endurance after three days of rest, 'provided their fatigue did not go below 0%'. In all cases, players do not suffer fatigue penalties until their fatigue falls below 50%. At 50%, players begin a steady decline in their ratings until 0%, where their ratings are reduced by 20% (10% for pitchers). Once a player’s endurance falls below 0% there is a more accelerated decline. Position players who reach -50% fatigue would be playing with their ratings reduced by 60% and there would be a 30% reduction for pitchers. All skills are effected by fatigue with the exception of EN and SY.
There are a few ways keep your players rested, aside from manually adjusting lineups between games.
A full baseball season can take its toll on a player. Players have limits as to how much they can participate in a season before they start suffering long-term fatigue penalties
How much a player can play is a factor of a player's Endurance. Players with the bare minimum Endurance (1) can play in about 50% of a team's games before suffering any sort of long-term penalties. Players with a high endurance (over 90) can play in nearly all of a team's games without issue. Season fatigue can set in early, or late in the season, depending on overuse of the player. The impact of the season fatigue depends on how overworked the player is and how long the player has been overworked.
'Example:' Player C has an Endurance of 50, which allows him to play in about 75% of his team's games without any adverse effect. Twenty games into the season, he's played in all 20 games. This is over the 75% limit, but since it's only been 20 games, the impact will be small (if not non-existent). However, if the player continues the pace the impact of season fatigue can grow.
You can offset season fatigue by resting a player to get him closer to his physical limits. If Player C from our example played 80 out of 80 games, he would be suffering some season fatigue, as he has played in 100% of his team's games halfway through the season (compared to his reasonable limit of 75%). However, if he played in 20 of his team's next 40 games, bringing him to 100 out of 120 games played, his season fatigue will go down.
Season fatigue can be very small or very dramatic, depending on the Endurance of a player and how much he is overworked. Most players with reasonable endurance will be able to play in the majority of their team's games with minimal impact.
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.
Whereas day-to-day fatigue reduces a player's current Endurance, season fatigue impacts two things:
The formula for season fatigue is complex, but takes into account a player's usage as compared to how far into the season it is. Players can be used lightly at the beginning of the season and play hard at the end to avoid suffering season fatigue. Similarly, players can be rested at the end of the season to get themselves a little extra rest (and less season fatigue) before the playoffs.