Rustiness in the playoffs is a factor almost every season in real life baseball. (i.e. The Braves always seem to beat an early round opponent quickly, and have to wait around a few extra days to see who they play, invairably giving some players extra rest days.) In PB, the same thing can happen. Keep in mind that "Rusty" is not always bad. It's just an additional randomizing factor that sometimes actually makes your players perform better.