How do the DP/FLEX, the extra player (EP) and batting the whole roster work?

Your lineup options in JO fastpitch (Rule 4, Sections 1, 3 and 4):

DP/FLEX:

• Declare it before the game. In JO play, the DP can be anywhere in the batting order and the FLEX (defense only) is listed last.
• The DP stays in the same batting spot all game and may play defense. If she plays defense for the FLEX, the FLEX has left the game and you're down to nine.
• The FLEX may bat in the DP's spot. That also takes you down to nine.
• Both the DP and the FLEX may re-enter once. Putting the FLEX into the batting order for anyone other than the DP makes her an illegal player.

EP: declare her before the game. She bats in a fixed spot all game, can play defense, and can be substituted for. If you start with an EP, you must use one all game.

Batting more than nine in pool play: extra batters are listed as EPs. If a player leaves for any reason other than injury or ejection, an out is recorded in her spot. If she leaves injured, her spot is skipped with no out. You can't play with fewer than eight.