In my experience it seems that rustiness seems to fade fairly quickly in a game situation. I seem to be able to avoid this though, by replacing players in the field in the top of the 9th with 2 outs and the game in hand. For pitchers, I usually use the IBB to get rid of rustiness at the close of a game. That way, the BFA doesn't go down for that pitcher but the rustiness is gone for the next game. Away games are, of course, a different story.