Understanding the ASA DP / DEFO Rule
Starting Lineup
With DP/DEFO, you have 10 starters, not 9. Both the DP and the DEFO are starting players. The DP/DEFO must be indicated on the starting lineup. Once the starting lineup has been given to the umpire, these positions cannot be added.
Batting Order / Substitutes
As with any lineup, a substitute bats where the player she replaced was batting.
DP/DEFO are joined at the hip with respect to the batting order. If both players are in the game, the DEFO has number 10 in the batting order (i.e. she does not bat). The only place in the batting order that either DP or the DEFO can bat is the place the DP occupied at the beginning of the game.
In a normal substitution, one player leaves the game and one player enters the game. However, swapping the DP/DEFO for each other is a "half substitution" that is, only one member of the pair officially leaves the game or officially re-enters the game.
For example, if the DP comes in on defense for the DEFO, the DEFO has left the game (the lineup goes from 10 to 9 players). If the DEFO re-enters on defense (which she can, 1 time), and the DP returns to offense only, the lineup goes back to 10 players. This move has not affected the DPs starter / substitution / re-entry status in any way.
Lets take the reverse example: If the DEFO comes in on offense for the DP, she is replacing the DP in the batting order (the lineup goes from 10 to 9). In this case, the DP is removed from the game, and the substitute re-entry rules apply to the DP. If the DP re-enters, she will re-assume her original position in the batting order, and the lineup will go from 9 to 10, and the DP will have used up her re-entry rights. The DEFO will return to playing defense only. This move has not affected the DEFOs starter / substitution / re-entry status in any way.
Either the DP or the DEFO can be substituted for in the usual ways by other players, but the substitute takes on the position of the DP or DEFO (depending on who she is substituting for).
Defensive Position Swaps Involving the DP and DEFO
As with any lineup, defensive position swaps are not substitutions.
The DP starts at the defensive position of "F10" - benchwarmer. This means you can swap the DP with any player
other than the DEFO on defense and no one has left the game; it is not a substitution.
The player removed from defense continues to bat in her normal place in the batting order.
The DEFO can be moved from her starting defensive position to any other defensive position (except for "F10" benchwarmer), and she remains the DEFO, and it is not a substitution.
Playing Shorthanded with DP/DEFO
The ASA rule is you can continue shorthanded with l fewer player that you started the game with. If you start with DP/DEFO, while your starting lineup was 10 players, only the offensive lineup counts for the shorthanded rule. This means with DP/DEFO you need 8 players offensively to continue the game, just as before.