After Derek Jeter posted the worst season of his career in 2010 (.320 wOBA), the consensus was that Jeter would likely have a moderate rebound season in 2011. The Fans projected for a .336 wOBA. Bill James, Marcel, CAIRO, PECOTA, and ZiPS all projected Jeter’s wOBA at a narrow band around that. The MSM was relatively quiet about Jeter’s precipitous fall, either apparently taking it for a fluke or because they refuse to ever question Derek. Randy Levine was so confident that Jeter would bounce back that he handed the 36-year old a 4-year contract.

Now, nearly a month into the season, hopes for a significant rebound are fading. The Captain has has been even worse than last year. Of course small sample size warnings apply, but his current .279 wOBA is solidly below replacement level.

Surprisingly, Jeter is walking at his career rate (9.6%) and has cut down a lot on strikeouts (8.3% K/9 compared to a career 16.8%). So, what is going on underneath the surface that is plaguing Jeter? Let’s take a look:

1. Bat Speed

Until last year, Jeter never swung at more than 22% of pitches out of the strike zone. Then in 2010, that number jumped to 28%. This year it has crept up to 29.6%. How bad is this in the context of the rest of the league? Strikeout King, Mark Reynolds, has never swung at more than 27.3% of pitches out of the zone.

At the same time, Jeter is swinging less at pitches in the strike zone. Jeter has been declining in this respect for years, and it reached a nadir last season, as he only swung at 67.2% of the pitches in the strike zone. This year it’s even less at 66.4%.

As a rule, batters’ pitch recognition generally improves as they age. After 15 big league seasons, it’s not as if Jeter has suddenly lost his ability to tell the difference between a fastball and a curveball. The likely explanation for these numbers is that Jeter has simply lost bat speed. Therefore, he needs to start his swing earlier, which means he needs to make the decision to swing or not before he has a good idea of where the ball is going.

It is unlikely Jeter can do much to correct this withering that time has wrought. The result will be a lower BABIP, as he swings at less choice pitches. It will also result in less power because he will not not be able to generate the bat speed to bring his anemic ISO (currently a jarring .024) back to his career average (.138).

2. Groundballs

Jeter has always had a groundball tilt to his swing, and this has only deepened in recent seasons. He has not hit less than 56% of balls on the ground since 2004. Last year his GB% swelled to 65.7%, well ahead of the 61.1% runner-up Elvis Andrus (he of zero 2010 HRs). A look at the names behind Jeter and Andrus (Bourn, Pierre, Schumaker) reveals the problem with hitting a lot of groundballs: they never find their way over the fence. They also result in rally-killing DPs — notorious Jeter bugaboo.

It is therefore alarming to see Jeter start the season hitting an astounding 75.3% of his balls on the ground. Groundballs go for hits more often than flyballs, but a GB rate that high indicates that Jeter is just weakly grounding out a whole lot (and anyone watching the games doesn’t need the stats to tell him that). He needs to hit the ball on more on a line if he is going to regain relevance at the plate.

3. Foot Speed

Jeter is an excellent baserunner, but he has never been the fastest guy. His recent speed scores put him in the company of smart baserunners who have slightly above average speed — Johnny Damon, Orlando Hudson, Aubrey Huff. As he enters his late 30′s, it is inevitable that Jeter will lose some speed, and this will hurt him more than most.

Jeter has managed to augment his BABIP (and therefore OBP) by legging out a bunch of infield singles each year. He ranked 3rd in infield hits in 2010. Going back from there, Jeter ranked 11th in ’09, 4th in ’08, and 3rd in ’07. If Jeter’s speed is in decline (which we would expect as he turns 37 in June), it will have a major impact on his wOBA, as both his OPB and stolen bases will suffer.

4. BABIP Mojo

The above-average speed and solid groundball swing helps explain why Jeter has the second highest career BABIP of active players (his .355 is one point shy of Ichiro’s .356). But, they don’t completely account for his being so many standard deviations above the crowd. Jeter has always had a knack for getting the ball to find its way past infielders’ gloves. Call it luck or call it skill — whatever it is, it has eluded Jeter as of late. The years of .370 and .380 and .390 BABIPs are gone. With the decline in the skills mentioned above, they are not coming back. Jeter’s BABIP was a career low .307 last year, and it has fallen to .282 in the early going this year.

This is the one area where we can hope for some positive regression from Derek. We don’t have a good handle on projecting BABIP, but Jeter is surely not a .280 BABIP guy. While you can’t project him to hit his career average here, there’s a decent chance he can can take some strides in that direction and surpass last year’s number.

Looking at the complete situation though, it is hard to paint a rosy picture of The Captain right now.

Data source: Derek Jeter’s Fangraphs Page