I think Peralta's defense has exposed a pretty serious shortcoming in the front office's strategy.
Just anecdotally, even apart from last night's error, you can see that Peralta is simply not a good defensive shortstop -- maybe not even an average one. And that obviously prompted the deal for AstroCab, who by all accounts is a plus-plus defender at either MI position, although he is at least a year, maybe two, away from the big-league roster.
Additionally, Marte is clearly a subpar defender at 3rd. I have not had a chance to watch him and I know error totals are far, far from the whole story, but he's making an error about once every four games. That's bad, folks.
A left side of the infield featuring Marte and Peralta would be a disaster defensively.
So what do you do? The only other position Peralta has played with any regularity besides SS is 3B. Move him to 3B, where he is at least less of a liability than he is at SS, and where do you put Marte? 1B being Garko's spot next season (I believe he's earned it, and they're both RH batters, and from what I've read Garko would be a better glove at first), the only real option is LF.
So now you've at least minimized the defensive problems in the infield, but that leaves two gaping holes at SS and 2B. I believe starting in 2008 AstroCab and Eider Torres could make a pretty nice MI combo (with the gloves at least, I doubt either will hit much at the major league level) but it would take some serious dealing by Shapiro to fill the middle infield for next year.
So what is the problem with the FO's strategy that I mentioned above? They have, at every opportunity, placed a premium on finding the best offense possible at each position, while almost completely ignoring defense. We have heard this argument in defense (so to speak) of keeping Martinez, Peralta, and Marte at their positions, even to the point of giving up a plus defender in Crisp to obtain Marte. Yes, Martinez's bat at C probably outweighs the cost of the steals he gives up, and yes, Peralta's offense (which I am not worried about in the long run) makes him a valuable shortstop.
But the problem with this analysis is that it looks at each of these cases on an individual basis, and what we're seeing is that defensive problems at multiple positions can combine and multiply and amplify each other -- and can clearly have adverse effects on our pitching, as we've seen recently with CC, Byrd, and last night, Lee.
So Shapiro has backed himself into a corner with this roster, and he needs to find a way to add some defensive prowess to it for next year. The only obviously open spot to do this is 2B, and I am sure they are hoping AstroCab's bat is good enough that they can carry him in this position. But even if that works out, the left side of the infield is still another defensive disaster waiting to happen unless he gets creative.