Updated THT team page:
To date, the Mariners have turned 19 fewer balls in play into outs than you'd expect given their groundballs/fly balls/line drives against. This has cost them ~15 runs and goes a long way towards explaining why the team ERA is higher than the team FIP despite a pretty good strand rate and a better-than-average number of infield flies. That's really bad.
Not convinced that defense matters? While screwing around at one point over the weekend, Matthew and I saw that the difference in BABIP against for the 2001 and 2007 Mariners was 57 points. Over a full season, 57 points of BABIP equals about 250 balls in play, or somewhere between 175-200 runs. 175-200 runs. From defense alone. Now, granted, the 2001 Mariners were kind of historically awesome with the glove, but the difference between even just a "normal" good and a "normal" bad defense can easily be 6-10 wins. That's huge. Just look at the Rays' turnaround - this sort of thing can make a world of difference.
Team defense is the most underrated aspect of the game today. I'm not sure exactly how many organizations "get it", but the Mariners very clearly do not, and it's killing them on the field. These guys don't score nearly enough runs to be able to justify giving them away for free with bad defense.
God dammit Yuni.