The following comment was posted by Will two days ago on Daedalus's blog.  (I have been unable to post comment/reply there from work, but will post there also once I have access.)

"Rich Aurilia as a shortstop: "

".244/.279/.415 "

"Correct me if I'm wrong, but the whole point of starting Aurilia at SS is for his bat, right? Well, he's hitting no better then Clayton or Castro at short, so why are we making a major sacrifice in defense if we aren't getting anything in return offensively?"

I'd like to tackle the Rich Aurilia question, not sure exactly what the answer is prior to looking up numbers....I'd imagine that overall, Aurilia is a MUCH better hitter.  

Aurilia's 2006 stat line is
286/335/518
Clayton is 266/312/349.  Clayton hasn't seen an OPS north of 700 since 2004, when he played in Colorado.  Prior to that was 708 in 2001.  Aurilia, with the exception of 2004, has been consistently over 700.  

So, offensively speaking in aggregate, Richie's bad years are better than Clayton's good years.  

Looking at their splits, I see the point regarding Aurilia's stats at SS.  Does playing SS cause Aurilia to hit worse?  I'm not sure how playing a particular position affects his batting, unless he spends all pre-game doing defensive drills and no time in the batting cage, and that somehow rubs off on him during the game.  

I think the past couple of weeks, when Richie plays SS it is vs a RH pitcher.  Hatteberg plays 1st, Richie plays SS.  Versus a LHP, Aurilia's been playing 1st and Clayton SS.  Interestingly, Aurilia's number at SS almost match his numbers vs RHP.  Clayton has been hitting LHP, and not been doing so well against RHP.  Their splits:

Clayton vsL: 342/395/432
Clayton vsR: 237/281/319

Aurilia vsL: 365/423/730
Aurilia vsR: 244/287/407
Aurilia at SS: 244/279/415

Offensively, vs righties, they are about the same, except Aurilia has about 100 more points in SLG.  We could debate whether the extra 100 points in slugging is worth Clayton's defense, but I think we'd have to debate first whether Clayton is better than Aurilia defensively.  By watching games over the past month and taking a quick glance at the year-to-date stats, I don't think there's much of a difference between how the two have handled SS so far this year.  

I'm not sure if we should expect Clayton to be better than Aurilia and that he's done statistically poor in a small sample size, or if Clayton has truly "lost a step" and they are fairly equal defensively.  

I did not specifically look into the details behind Aurilia vs Castro, but I would expect to find Castro to have better defense than Clayton and even worse offensive numbers.  Producing less offensive production than Royce Clayton is how you become a late-inning defensive replacement.