During a recent conversation with my (huge Yankee fan) father-in-law, I extolled the virtues of Mark Teixeria, especially his defense, citing how poor Jason Giambi was in that area. Not only will Tex hit about as well as Giambi, but he'll make more plays in the field as well. I said Tex is probably our best defensive first-baseman since at least Tino Martinez (not counting the stop-gaps of Travis Lee, Tony Clark and Doug Mxyzptlk). As it turns out, he's our best since Don Mattingly.
The only defensive stats that go back to the 1980s are Range Factor and FRAA (Fielding Runs Above Average), courtesy of BRef and BPro.
Mattingly saved 33 runs above average during his career, with his top year being 1992 (8 FRAA).
Tex is four runs below average for his career, but he may have turned a corner in 2008, saving nine runs, which is more than Donnie ever did.
Range Factor basically tells us the number of plays (e.g. outs) made per game.
Jason Giambi was not horrible, just below average. With the Yankees, he's been anywhere from average to safely below. For his total career he's been an average defensive first-baseman (mostly due to how good he was in Oakland).
Tino Martinez was well above average for most of his Yankee tenure, usually making 2-3 more plays per game than an average first-baseman. For his major league career, he made about 1 1/2 more plays per game.
Mark Teixeira has ranged from above average to phenomenal in his career (especially in 2006, when he made about 3 1/2 more plays per game than average). Overall, he makes about two more plays per game than average.
Donnie never had a single defensive year as great as Tex's '06, but was consistently well above average for all 14 seasons of his career. For his career, he made about two more plays per game than average.
The newest statistical measurements also shine brightly on Teixeira's defense. UZR (ultimate zone rating) had Tex as the third best defensive first-baseman in MLB in 2008, behind only Lance Berkman and Albert Pujols.
As Jeter and Arod age, and their defense suffers, the acquisition of Teixeira will alleviate a significant portion of their declining defensive abilities.