How many players do we need, and how does the extra player (EP) work?

Lineup (Rule 4, Section 1): slow pitch uses 10 defensive players: pitcher, catcher, four infielders and four outfielders (left, left-center, right-center and right).

Extra player (Rule 4, Section 4):

• An EP is optional. If you use one, list the EP in the batting order before the game, and keep one for the whole game.
• With an EP, all 11 bat and any 10 of the 11 can play defense.
• The EP stays in the same batting spot all game, can be substituted for, and may re-enter once.

Re-entry: any player may leave and re-enter once, in the same spot in the batting order.

Shorthanded rule: you can start or finish with one fewer than the required number. The empty spot goes last in the batting order and is an automatic out each time it comes up. During a game you can continue one short if a player leaves for any reason other than ejection, but you can never bat fewer than:

A player who leaves can't return (except under the blood rule). A substitute who arrives must go straight into the empty spot.