Is it weird that Derek Jeter is so polarizing? Probably not. I mean, he is the most recognizable face on possibly the most loved/hated/loved-to-hated sports franchises in the world (no one loves to hate the Red Sox, right? They have their fans, and everyone else despises them. Despises Red Sox fans, I mean.), so I guess it isn’t surprising. (No, I’m not talking about that “other stuff” that recently came up. Dustin covered that other stuff earlier, which is great, because that means I do not have to mention it.).

Still, while everyone agrees that overall he’s been a great player, we can’t seem to figure out how great. On one hand, there is the issue of fielding. It took a long, long time, but pretty much everyone now agrees that Jeter has generally been, at best, a below-average fielder. Exactly just how far below average depends on whom you ask and which fielding metric you prefer. That generates a lot of the debate: is he one of the best shortstops of all time with a bat that made up for a subpar glove, or has his fielding been so bad that despite his bat he’s a borderline Hall of Famer who gets a boost from all the postseason memories?

Leaving the fielding and Hall of Fame debates (both well-worn, but hey, it’s the Sports Nerdsosphere, if something is worth doing, it’s worth overdoing) aside, though, check out that bat. Yeah, Jeter’s a good hitter. Very good. And after two rough years (relatively speaking), at 38 he is hitting well again. It isn’t vintage, late-90s Jeter, but it’s very good. No, he shouldn’t be an MVP candidate – even if you ignore fielding complete, teammate Robinson Cano has had a better season -but it is a heck of a year.

But even Jeter having a good season is not of particular interest in itself. It is how he is doing it. It is not that he is defying Father Time in general, it is the specifically weird way in which he is doing so.

Obvious point: everybody ages differently, and that is as true of protein shake-drinking athletes who sit around wondering if the clubbies remember to destroy their “spare” cell phones as it is of pop-tart eating bloggers who sit around wondering if some jackass TV personality is going to fill them with rage this week. So when we talk about player” aging curves, we have to remember that we are talking about the “typical” hitter — just as when we talk about whether or not a player is likely to regress, we have to go off limited information in order to regress him to the correct population. Now, aging curves themselves are subject to plenty of controversy within the “sabermetric community,” and I will not re-hash all of those. Tom Tango has some valuable selections of discussions on aging here. They are a bit long in the tooth, but one can learn a great deal from them.

When we talk about a player “defying Father Time” (sorry, my ability to think up cliches is in its decline phase), we all know what that means: man, he’s old, but he’s still good. Jeter’s general case is a little more specific, but not all that unusual. After a (final?) near-MVP-level performance in 2009 (134 wRC+, 71. fWAR), Jeter’s bat took a dive in 2010 to 94 wRC+, the worst full season number of his career. That led to some ugly contract negotiations in the off-season, but it got done. Jeter was a little better in 2011 (104 wRC+), but the End Was In Sight.

Right?

Well, here we are in 2012 and while Jeter has cooled off enough¬†that talk of a 2009 repeat is silly, he’s still having a nice year with the bat, especially for a shortstop (he’s been awful with the glove, but remember that we aren’t dealing with that here): .325/.364/.350 for a 122 wRC+. It is surprising, but those numbers are not mind-blowing all by themselves. Jeter is a world-class athlete, after all. It is not as if he has never been good before. But if we look a bit closer, things get weird.

Let’s take a roundabout but perhaps more simple way of setting this up by discussing¬†old player skills. In short, the idea of “old players skills” as originally formulated for the public by Bill James (I think) and refined by others is that younger players who are on the slow side and have relatively low batting averages, high walk rates, high strikeout rates, and good power, “peak” earlier than other players, and thus also decline at an earlier age. In practical terms, if the average major league hitter typically peak at 27, a 25-year old having a big year usually is someone who still has some “upside.” However, if that 25-year-old is a big fat first baseman who can’t run, strikes outs a ton, but managed to provide good value with a bunch of walks and home runs, one might be a bit wary about giving him a big extension.

That assumes the older players skills “theory” is true — I have to admit I tend to be somewhat skeptical. In any case, I am simply using it here to illustrate something about how hitters generally age. Derek Jeter has obviously never been one associated with any of the facets of being an old player, certainly not in his younger years. But the reason those skills are called “old player skills” is because they capture how players generally age.

As they get older, players typically hit for a lower average on balls in play, strike out more often, and slow down. On the other hand, isolated power peaks a bit later (to be more precise: home runs and extra base hits on contact decline in the late-20s, but do so later and at a slower rate than hits on balls in play and contact, thus isolated power does increase) and walk rate increases almost throughout a player’s career.

Some players can make this work for them. Frank Thomas, although he was always slow, was certainly not an “old player” stereotype in the early part of his career. During his monstrous (and weirdly underrated) 1990s, he only had a strikeout rate over 15 percent once, and was around 11 percent most years. He always hit over .300. In the early 2000s, with age an injury bugs taking their toll, Thomas had lost some bat speed, and his strikeout rates went up. However, he kept his walk rates high and kept hitting for good isolated power and still managed some very valuable seasons not just for the White Sox, but also for the 2006 A’s and 2007 Blue Jays.

Which brings us back to Derek Jeter. What is so weird about Derek Jeter at 38 is that he has quite clearly not followed the Frank Thomas model for aging gracefully. Jeter has obviously lost a step: he stole 30 bases back in 2009, 18 in 2010, 16 in 2011, and only 9 so far this year. Jeter does have a high BABIP his year, but that is at least a bit surprising… as he also had it in 2009 (.368), then it dropped in 2010 (.307) but came back up a in 2011 (.336) and then to his year’s .351. Not what we would expect from a player in his mid–to-late 30s, even from a guy like Jeter who has been able to maintain a higher-than-average BABIP for pretty much his entire career.

Of course, BABIP varies more widely from year-to-year than other stats, so it one might expect it to bounce around. But more “stable” stats that we might expect to follow more typical aging curves are, if anything, even more puzzling. This is perhaps best illustrated by walks and strikeouts, which are usually subject to less random variation year-to-year than other stats.

Jeter has always been able to make contact. And in his big 2009 season, he has a good year even by his own standards with a 12.6 percent strikeout rate. He seemed to follow the curve in 2010, when it went up a bit to 14.3 percent. But then in 2011 it went down to 13.3 percent, and this season Jeter has struck out in less than 12 percent of his plate appearances to date.

Jeter’s walk rate is even more at odds with what one expects from an aging player. Jeter has never walked all that much, and his 10.1 percent walk rate in 2009 was only the fifth season of his career in double digits. Part of the reason he had such poor seasons in 2010 and 2011 was that his walk rate dropped even below his (current) career average of 8.7 percent to 8.5 and 7.6 percent, respectively. So has part of this 2012′s success been Jeter coming to terms with his age and being a bit more patient? Uh, no. He’s currently sitting on a 5.3 percent walk rate, pretty easily the lowest of his career.

Indeed, Jeter’s weird aging with respect to the most “solid” peripherals — walks and strikeouts — extends pretty much for his entire career. For strikeouts, we would generally expect a player to lower his strikeout rate until his mid 20s, at which time they should go up. Walks should generally go up slowly his whole career. Here is are graphs of Jeter’s trajectories (Courtesy of FanGraphs; keep in mind that they include his 51 PA cup of coffee in 1995, so ignore that year):

While Jeter’s walk rate does seem to have gotten slightly better in his 30s before the recent bout of hackiness, if anything his strikeout rate has been slightly better as he aged. It only serves to drive the point home: in recent years, both good and bad, Jeter has generally done the opposite of what the typical player does at this age.

It is true that there simply are not that many 38-year-old hitters, especially not everyday shortstops (no matter how poor their fielding is). Love him, hate him, or strangely indifferent to Jeter, everyone would agree that he is hardly typical. We know that aging curves are generalizations with all the problems and qualifications that entails. Of course some players are going to defy those generalizations. But again, it is the way that Jeter is doing it that is so curious: he is not just playing better at 38 than at 36 and 37, but he seems to be doing to by being “immature” as a hitter.

Does his impact how we should look at player aging curves generally beyond reminding us of their limits? No. One exceptional player should not drive us to do anything. Nor do I know what this means for Jeter going forward. But it sure is weird, or at least interesting to think about.