I'm not sure if this is a serious question, since the answer is so obvious. In the late innings, when you've already scored enough runs to win, it makes sense to put in the guy that will do the best job of preventing runs from scoring. In the early innings, obviously the light-hitting, all defense guy is a bigger liability than the guy that can hit but plays inferior defense. Of course it is a serious question. It makes no logical sense whatsoever. What does it matter that the poor defensive player lets in runs at the beginning or end of the game? But more to the point, how often does his replacement prevent a run from scoring in the 8th or 9th inning? Are you honestly saying you don't understand the logic behind why a manager might substitute a Doug Mientkiewitz for a Craig Wilson in the 9th inning with a 1-run lead? The premise is elementary: when you need your defense to hold the lead and secure the win, then you put your best defensive players in the game. It's a basic principle that applies to many sports. You can agree or disagree with the wisdom of such a strategy as it applies to baseball, but to fail to grasp the logic is pretty puzzling. It's pretty basic stuff. Defense doesn't matter. :D :D