Where Jordan Zimmermann Is Trending Up

With Jordan Zimmermann, it’s so easy to focus on the downside. You’ve got a pitcher, coming up on 30, who’s already had Tommy John surgery once. He just posted a second-half ERA north of 4 despite playing in a woeful division, and he just lost a bunch of strikeouts, and he also just lost some fastball velocity. Every pitcher has red flags, and Zimmermann might have one or two more than usual. We’re all to some extent risk-averse, so it might not immediately seem like a great idea to guarantee Zimmermann $110 million over five years. In an ideal world, you’d like a bit more certainty.

Not that there’s ever such a thing as certainty. Someone as certain as, say, Carl Crawford dropped 8 WAR in between leaving the Rays for the Red Sox. Certainty is a lie, and beyond that, it’s not like Zimmermann wasn’t most recently good. By whatever measure, he had a three-win season. It was his fifth in a row. Zimmermann does actually seem fairly steady, even if you figure he peaked in 2014.

And underneath, Zimmermann has something going on. Most people are concerned with what’s physically going on. And, admittedly, what I’m going to highlight has an unclear link to ultimate performance. But Zimmermann has been changing himself, and in one way, he continued something he began two years ago.

You probably have some idea of Zimmermann’s career path. He’s long been a pretty good pitcher, but a couple years ago, he was a really good pitcher, with his first sub-3 FIP, and his lowest ERA, and his greatest strikeout rate since surgery. Just last year, Zimmermann seemingly gave his progress back, and there’s a parallel between Zimmermann’s performance and his rate of fastballs thrown. Borrowing from Brooks Baseball, here’s his pitch mix over five years:

Zimmermann, mostly, has sat in the low 60s. In 2014, he shot up to around 70. He just went back to his old norm. Between 2013 and 2014, there were 129 starting pitchers who threw at least 50 innings in each season, and Zimmermann had the 11th-greatest fastball-rate increase. Between 2014 and 2015, there were 129 starting pitchers who threw at least 50 innings in each season, and Zimmermann had the 11th-greatest fastball-rate decrease. Zimmermann returned eight percentage points of fastballs, also losing eight-tenths of a tick of fastball velocity, and so the takeaway seems like Zimmermann just had a 2014 career year and now he’s settled into something below that, something familiar.

It’s just, not everything from 2014 has been reversed. In a lot of ways, Zimmermann just went up and down, but now look at his fastball heat maps, from the last five years, borrowed from Baseball Savant. These are plots of Zimmermann’s four-seamers:

It helps if you know what to look for, and maybe it’s subtle, but you can see that, in 2014, the fastballs got a little higher. And in 2015, they got higher still. Zimmermann throws the overwhelming majority of his fastballs in the upper half, and last season he kept that up. In truth, he did it even more. In this table, see Zimmermann’s rates of high fastballs thrown, where “high” is defined as above the middle of the zone. Then you see Zimmermann’s MLB rank, and the number of qualifying pitchers with enough fastballs offered (minimum 1,000).

Zimmermann’s always been a high-fastball kind of guy. Even before 2014, he’d rank around the upper tenth, elevating three of every five heaters. But then he moved to two of every three, and most recently, he moved to three of every four. Zimmermann just elevated three-quarters of his fastballs, not just finishing in first in the category, but finishing in first by a full five percentage points over Madison Bumgarner and Jake Odorizzi. Zimmermann blew the field away, in attacking the upper portion of the zone with his heat.

And it’s not like Zimmermann’s fastball carries a ton of backspin. Those fastballs are said to “rise” and you usually see them up. Zimmermann’s fastball is a little more ordinary in that regard, but still he likes to stay around the belt. This is a table of last year’s most similar right-handed four-seam fastballs to Zimmermann’s, thrown by starting pitchers. You see some average pitch traits, and then a measure of height, in inches, above or below the middle of the PITCHf/x strike zone.

Zimmermann’s average four-seamer was about six inches above the middle of the zone. The highest among the comps is just above four inches, and the average of them is +2.2 inches. So, of the fastball comps, the average heater was located 2.2 inches above the middle of the zone. Zimmermann cleared that by almost four inches. He worked up more than anyone else, and so it follows that he also worked up more than the starting pitchers with similar fastballs.

It causes you to wonder. Zimmermann more or less returned to what he used to be. Yet he used his fastball quite differently. And, more than that — his fastball performed an awful lot worse. By pitch values, in 2014, Zimmermann’s fastball ranked in the 89th percentile. Over the three years between 2012 and 2014, it ranked in the 88th percentile. Last year, it ranked in the 33rd. Zimmermann kept throwing his fastball higher, but it got him in more trouble. He did lose a little velocity, but nothing dramatic, nothing that, say, knocked him below the league average. He was still regularly throwing 93-94.

But in any case, Zimmermann’s fastball let him down. He still overall had a strong season, but he squeezed more out of his breaking balls. I don’t know what the explanation would be. Maybe hitters were just more often sitting on the fastball. Zimmermann’s curveball rate was his highest since his injury-shortened 2010. The curve was good, and the slider was good, so Zimmermann was good, just differently good from before. He kept trying a certain strategy with his fastball while simultaneously de-emphasizing the pitch.

So now we wait to see what comes next, and as easy as it is to observe that Zimmermann has lost some fastball power, he just had his best-ever slider velocity. He had his best-ever curveball velocity. He hasn’t lost strength across the board; it seems he’s maybe just lost peak strength, and there’s some chance that’s just mechanical. And it also doesn’t seem likely that Zimmermann’s fastball is now suddenly a weakness, having lost less than one tick. He’s aggressive with the pitch up, more than ever before, and that ought to work for him, if only because it always did. Maybe he got to throwing the pitch too much up. Could be he crossed a threshold. But it wouldn’t be baseball if a player didn’t need to think about his adjustments. Even a nine-figure player.