I've been trying to make double headers work with OOTP for some time, but it has become obvious that a couple things need to be adjusted with OOTP before this can happen. Fortunately, it does not appear that the required adjustments are too extreme.
Please see the following thread for more details on my research into the problem:
http://www.ootpdevelopments.com/boar...r&pagenumber=3
The most immediate fix that would go a long way toward addressing the issues with doubleheaders would be to record fatigue at the end of the game rather than at the end of the day. It does appear that the pitching rotation pointer is modified once the starting pitcher is identified, either before or after the game.
Once fatigue is handled, it would be useful to tweak the algorithm for starting pitcher selection. The default rotation mode appears to be to use the highest rested starter with the only alternative being strict order. Assuming that fatigue is recorded at the end of the game, then it is possible that all of the pitchers in the starting rotation would be fatigued. In that case, I would like to see the spot starter preferred if rested. After that, other pitchers should be preferred over fatigued starters. Maybe this mode could be "only rested starters" or something like that. If you look at starting pitcher use, you will see that most teams use more than 5 or 6 starters over the course of the season while in OOTP I have seen more clustering of starts.
I would also like to see the game engine and schedule engines recognize double headers. For instance, if the game notices two games between the same team on the same day (even if they are at different times), it should make note of it. If the start times are identical or separated by less than say 5 or 6 hours, the matchup should be considered a doubleheader, allowing a single attendance figure for both games and perhaps a slight bump in attendance due to the improved "value" or interest for fans. A gap of 5 or 6 hours could be treated as a day-night double header, with two different gates for the home team.
Finally, by noticing doubleheaders, start times could be calculated for the second game based on when the first game is finished. For instance, starting the second game 30 minutes after the first game ends. This could be used to address the problem encountered with simming doubleheaders in the background while playing out a game--this is the situation where statistics for one of the games in a doubleheader are not recorded.
Adding basic recognition for doubleheaders could help with a couple other issues. First, a doubleheader could be indicated on team schedules somehow. Also, the schedule editor and schedule reports could indicate possible errors, such as a team being included in two different matchups (not unprecedented, but usually an error in schedule creation) or a triple header (not unprecedented either but exceedingly rare).
I have been checking on this issue for a couple years now. I have found that lack of support for doubleheaders is the one cluster of issues that keeps me from completely enjoying the game. My particular interest with OOTP is trying to simulate the patterns of historical major league baseball with fictional leagues.