[Le Grande Orange]

OOTP cannot quite recreate the current real-life rules, which state that a postponed game made up in the other club's park has that other club bat first, even though it is playing in its own park. From your example, in real life, if Chicago at Atlanta is postponed, and the game cannot be made up in Atlanta, then the game is made up in Chicago, i.e.. Atlanta at Chicago. However, even though the game is taking place in Chicago, the Cubs would bat first in the makeup game.

This was a rule change implemented in 2007. Prior to then, the makeup game, Atlanta at Chicago, would be played as that with the Cubs batting second, with the team getting an extra home game for the season. MLB decided that was unfair, and by making the Cubs bat first in the makeup game, it's as if the game was being played in Atlanta, even though it is not. In other words, if home and away games are measured by whether a club bats first or second, rather than the park in which the game takes place, having the Cubs bat first keeps the proper totals in balance.

Note that attendance and revenue for such 'home team bats first' games goes toward the team in whose park the game is being played. Although the rule was adopted in 2007, it has only happened a few times. Most postponed games are made up in the park in which they were originally postponed.

From your example, OOTP ideally should list the makeup game as Atlanta at Chicago, but with Chicago batting first in that game (and that game only; the other games of the series would be played as normal). But OOTP can't do that, and because for financial system reasons all clubs need to have their full slate of home games, OOTP handles it the way you saw.