The Mariners are near the halfway point in the season (this somehow strikes me as both too high and too low. Baseball's almost half over already? Noooo. This shitty season's not even half over already? Noooo.) and it's been awhile since we've looked at how the defense is performing so let us take a quick dive into it.
First off, the Plus/Minus rating has us at 44 plays below average, putting us on a 94 play projection. That means we're 35 runs below average so far and on pace to surrender another 40 against average the rest of the way.
Our .677 DER is now 29th in baseball (AL avg .698) as the Pirates have managed to out not-field us to the tune of a tenth of a percentage point. However, the Pirate pitchers are responsible for some of that number while the Mariner pitchers have actually offered up more fieldable balls in play and thus our -44 rating is a solid dead last, 8 worse than the Pirates.
Going by RZR, the infield doesn't appear to be the brunt of the problem. They do have a lower than average RZR (.767 to .782) which through nearly half a season represents about 10-12 fewer plays on balls in zone, but they compensate by recording nine more plays out of zone than average so on the whole, it roughly balances out, though they are still a touch below average.
Looking at positional rankings: Sexson is predictably bad, Lopez is suitable and Beltre has something weird going on where he's nearly dead last on plays in zone but first in plays out of zone suggesting to me that either the zones are off or Beltre positions himself oddly compared to other third basemen.
The real culprit is Yuni who is now not even a shell of his former self but rather just an illusion like an after image burned into your cornea after looking at the sun. He has the 4th worst RZR and the worst OOZ among qualified SS. Flat out, he's been terrible in the field. We know Sexson is going to be gone by 2009. If the Mariners can still get inflated value for Yuni, they should probably take it.
However the outfield is a whopping two percentage points below average (.876 to .896), which translates to again about 10 plays (fewer balls in zone to OF than IF), but they are also 11 plays under the average out of zone number putting them around 20 plays (or more) below average overall. And these are OF plays so their run value is higher than the 0.8 you'd use for overall analysis, in fact it's a lot closer to 1.
Getting Reed and Ichiro in the same outfield full time would be a positive step forward for next year and preferably in LF and CF. I have no idea why Ichiro is back in RF. He was an asset in center field, I don't care what UZR says, and he's less of one in RF simply because there are less balls that are hit his way much less factoring in the relative positional scarcity and where his bat plays best.