Interestingly, this season, Jeter has made the crowds look wise and all of the idiots who were talking about the demise of Derek's defense (ahem, myself included), look somewhat foolish. Bryan Hoch of MLB.com recently took a deeper look into Jeter's play at shortstop this season and attempted to explain how his Ultimate Zone Rating has increased at age 35 to it's highest level since they began tracking UZR in 2002:
Thanks to a number of variables, Jeter has continued to find ways to turn back the hands of time defensively this year. He continued to follow the program outlined by Yankees strength and conditioning coach Dana Cavalea, but he has also been assisted by aggressive defensive positioning on the part of infield coach Mick Kelleher.While player's defensive performance is certain to vary from year to year, it seems less likely for someone to have a sudden improvement in their fielding in their mid-30's than it would be for them to have a career year at the plate. With defense, the outcomes are mostly binary; the play either gets made or it doesn't. With offense, there are vary degrees of success or failure a batter can attain, ranging from a double play to a home run, creating a wider gap between failure and success. Luck is also a bigger factor for hitters as they can't control where a batted ball goes to anywhere near the extend a fielder can position themselves to catch one.
Better health has also been a factor, as Cashman said there was "no doubt" at times that Jeter's health inhibited him in past seasons. So has adding a Gold Glove first baseman and receptive target in Mark Teixeira.
There is also an inherent assumption that defense is the bastion of the young and agile. It's based on quickness, agility and reaction time, all attributes which inevitably fade with age. Production at the plate can improve with patience, power and experience, most of which players do not possess when they first enter the league.
So how is it that Jeter is enjoying this renaissance now?
Of Hoch's four points above, one stands out as being the most significant: His positioning. UZR is calculated by dividing the field into 64 zones, and tracking whether or not players get to balls in what areas of the field. If Jeter is in fact being positioned better, which David Pinto also believes, it's going to appear that his range is increased when in fact he simply doesn't have to cover as much territory as he once did. (See here for a hilarious anecdote by the legendary Repoz of BBTF.)
Teixeria's glove probably helps, but Jeter has never made many throwing errors. He is on pace for 5 this year and has averaged 6.5 per season since 2001. His arm isn't the issue. I'm sure his improved health and conditioning regiment (which was intended to improve his explosiveness and lateral agility) have helped as well.
However, it's much easier to believe that Jeter is simply in better position to field balls hit his way than it is to think the Yankees hold the secret to a rejuvenating exercise program, or that he was playing badly injured over the last 8 seasons. Which is most certainly a good thing, because defensive positioning is much easier to control than health or lateral agility.