At all times, you must have at least 24 players and no more than 28 players on your roster.
You must have at least 13 and no more than 17 hitters. At least two of those hitters must be eligible to play catcher.
You must have at least 10 and no more than 12 pitchers.
You must have at least 5 pitchers who have starting pitcher Endurance ratings (for example: S7).
You must have at least 4 pitchers who are "pure" relievers (i.e. a relief rating (e.g. R2) but no starter rating).
You must have at least 1 pitcher who has a closer Endurance rating (e.g. C4).