The Coach's Office displays each player's condition from 0% to 100% where 100% is no fatigue and 0% is completely exhausted.
If a player is fatigued you may want to rest him for a few games. The amount of rest needed depends on the player and what condition he is in.
A player's condition is calculated by comparing total real life minutes to the total SimLeague minutes based on the current minutes per game projected to 82 games.
Make sure to take total minutes into account when drafting. For seasons where teams played fewer than 82 games, players are given credit for total minutes prorated to 82 games. So a player who played 20 minutes every game in an 82 game season is equal to a player who played 20 minutes every game in a 50 game season.
The fatigue percent is approximately the percentage of performance you can expect from the player. Fatigue effects nearly every aspect of player performance.