The market for starting pitching this offseason should be robust. I find starting articles with sentences that use words like “market” and “robust” is a great way to weed out readers. So, if you’re still with me, welcome to an article about Jordan Zimmermann!

The Zimmermann I’m referring to, by the way, is the Zimmermann that pitches, not the Zimmerman who hits. The Nationals are lousy with Zimmermen(n) so it’s easy to get confused. This particular Zimmermann, the subject of this here article, will be a free agent next season. After his big 2014 season, the Nationals talked to Zimmermann’s people (when you’re about to be a big money free agent you get you own people) about a contract extension to stay in DC beyond 2015 when his contract expired, but those talks didn’t get anywhere and then last off-season the Nats signed Max Scherzer. They did that because who doesn’t love a SuperRotation, but also as a replacement ace, as the club believed Zimmermann and to a lesser extent Doug Fister weren’t likely to stay in Washington after 2015. I don’t know what figures were discussed between Zimmermann’s people and the Nationals but it’s fair to say by not signing, Zimmermann passed on a lot of money.

Now, one half season into that decision and a half season from free agency, I wanted to take a look at Zimmermann to see how his decision is panning out.

Zimmermann had been a good 3.5 win starter on average through the first three full seasons of his career. He got some grounders, he kept the ball in the park, he limited walks, but he was never much of a strikeout guy. He had velocity on his fastball, sticking around 93 or 94 mph, above average for a starting pitcher, but aside from his first half season in the majors, the strikeouts remained below average.

All the other ingredients were there to become a front of the rotation pitcher. Except the strikeouts. But that’s kind of important, right? Without strikeouts, pitchers are playrooms with drop ceilings. They’re nice, they’re fun, but they’re not as good as they could be because you just can’t bounce a ball around in one except that time Jimmy Rendene did and smashed the basketball through the ceiling and what we all thought was asbestos rained down on us and oh man was Jimmy’s dad pissed. Sol: great pitchers need to strike hitters out at an above average rate or Jimmy’s dad is going to come royally unglued. Also they can’t become an ace.

We’ll call this Zimmermann’s Dilemma. Then, last season, he solved it! Poof! His strikeout rates went from a career 7.2 K/9 to 8.2. That’s a good jump, but it actually undersells it a bit. In has career through 2013, Zimmermann struck out 19.5 percent of the batters he faced, with more recent seasons being lower than that. Then, in 2014, he jumped to 22.8 percent. League average for starters in 2014 was 19.4 percent (previous seasons had been as much as 2.3 percent lower). So in one season, Jordan Zimmermann went from a below average strikeout pitcher to an above average strikeout starter. He maintained all the other things he does well too, with a notable dip in his walk rate as well. The end result was 5.3 WAR, a top of the rotation starter.

That brings us up to this season. The good news is Zimmermann has still been a very valuable pitcher (he’s currently at 2.3 WAR for the season). The bad news is the strikeouts are gone. He’s striking out 17.5 percent of the batters he faces, which would be the lowest percentage of his career by 1.1 percent if he continues it through the season. Essentially he’s lost whatever it was that made him so good in 2014. He’s gone back to being the pre-2014 Jordan Zimmermann. That’s a very good pitcher, but it’s not an elite one.

I wanted to see why Zimmermann’s strikeouts have dropped, but to do so I first had to understand why they spiked. I had an idea that maybe Zimmermann had received an undue amount of called strike threes in 2014. Strikeouts looking are notoriously unreliable year-to-year, but as it turns out, that wasn’t the issue. Zimmermann got 23.1 percent of his strikeouts looking in 2014. He’s got 22.2 percent of his strikeouts looking this season. That’s not even one full strikeout’s worth of difference. So nope.

As it turns out, the big difference came in the success Zimmermann had with his four-seam fastball. Check out this chart which shows the raw number of whiffs Zimmermann generated from his different pitches (courtesy Brooks Baseball).

Now, Zimmermann throws his fastball a lot, almost 71 percent last season, so the straight total of swings and misses is a big one. (That number was a career high and he’s sense corrected back towards his career norms this season by throwing it only 63 percent of the time.) Still, it’s a bit baffling as to why hitters would not be able to handle Zimmermann’s fastball in 2014 but be able to handle it much better in 2015. The average vertical movement on his fastball last season was 8.7. This season it’s 8.21. The average horizontal movement on his fastball last season was -3.81, this season it’s 4.51. It would appear Zimmermann’s four seamer has traded in some drop for some run. Those numbers are different but not so drastically different that you’d think they’d turn an above average strikeout pitcher into a below average one.

Percentage-wise that jump in swinging and missing at the four seem fastball looks a bit more tame and, instead, you can see the success he had in making batters swing and miss at his slider in 2014.

But even that has taken a step back this season. Again with the slider, the average movement is different but not drastically so.

One possible explanation is Zimmermann’s fastball velocity, which has dropped this season from an average of 94.58 mph last season to an average of 93.48 mph this season. What makes that explanation difficult to believe is that Zimmermann was throwing 2014 hard in 2013 and 2012 also but didn’t have the swing and miss success with the four seam fastball then. So, again, why 2014?

Jordan Zimmermann is still an excellent pitcher. But until the Tale of the Missing Strikeouts is answered, and preferably on the field, Zimmermann is looking at less earning power on the free agent market than we thought last off-season.