Rafael Devers has struggled against the fastball this year.

This was first brought to my attention by Six Man Rotation’s fantasy writer, Austin Perodeau, about a week or two back. As a Sox fan myself, I’ve watched Devers struggle. It’s noticeable, but I hadn’t known it was against the fastball specifically. I asked Austin if he had dug up any info on the matter that I could “borrow” for this article, but he hadn’t gone hunting for an answer quite yet. “I didn’t figure out why, just [saw] that he sucked,” he told me.

That observation was obviously correct. Against fastballs this season (through 6/12), Devers has hit just .197 with a .385 slugging percentage and a 33.3% strikeout rate, according to Baseball Savant. His expected stats (xStats) based on quality of contact (exit velocity, launch angle), are slightly better, but not by much, insinuating that, no, Devers is not simply getting unlucky; he has been just plain bad vs. fastballs. Brooks Baseball reaffirmed this, with this quick little summary of Devers on the front of his player page:

“Disastrously high” is the descriptor that Brooks used to describe his swing-and-miss tendencies against the fastball, and although harsh, it isn’t untrue. Devers’ 64 swing and misses on fastballs is tied for 4th in baseball with teammate Jackie Bradley Jr. While this may not be new for JBJ, this is new for Devers, who didn’t struggle nearly as bad with velocity last season:

Below is one of many plate appearances where Devers had a poor result against the fastball:

Austin Pruitt jams Devers a bit and causes him to fly out to center with the bases loaded. Why this is important is because, well, it wasn’t an incredibly hard pitch to hit. Ever since he was a prospect, Pruitt’s fastball velocity has been criticized. From Baseball America in 2016, “his poor fastball velocity leaves him vulnerable when his command or offspeed offerings aren’t at their best.” This particular pitch was clearly put exactly where Pruitt wanted it to go, so that command was present, but at 91 MPH with very little movement, that same vulnerability was also present, and it’s a pitch that Devers was visually upset about missing.

Nonetheless, Pruitt hit his spot up in the zone and got the crucial out. That area, in particular, has been tough for Devers, which allowed Pruitt to be successful. Below is a heat map of how often Devers swings at a fastball by zone:

As they should be, all fastballs in the zone are being swung at a good amount. However, there is a little bit of a bolder red in the upper third and it seems he may even be expanding the strike zone high a little bit. This is especially concerning because of how little quality contact is resulting from those swings. Here’s how often Devers swings and whiffs by zone…

…and here is his batting average by zone…

That’s a lot of red up in the zone on the whiffs chart and a lot of blue up in the zone on the batting average chart. In full, Devers is swinging at high fastballs more than any other location, but is swinging and missing a lot, and when he does make contact, the balls in play aren’t falling for hits, which most likely means bad contact.

That’s where J.D. Martinez comes in.

J.D. Martinez knows a little something about crushing high, low-90s fastballs, and after working with J.D. all weekend, Devers homered Tuesday night… on a 91 MPH fastball up in the zone.

Watch here.

Immediately, there’s something very noticeably different about Devers’ setup.

In the Pruitt pop-out on May 22nd (left), Devers has a very open stance, with his front foot about 12” away from the edge of the box, a stance he’s had his entire career. During the homerun on Tuesday night (right), Devers’ stance is much more closed, as that front foot is essentially right in line with the back. We’ve seen recent examples of MLB superstars benefiting from continuing to close off their stance, so maybe it can work for Devers too.

For Devers, what closing off his stance allows him to do is to “step in the bucket” less. Stepping in the bucket is a hitting term used to describe the direction your front foot goes while you stride. For a left handed hitter like Devers, this means striding out towards second base instead of directly to the pitcher, which causes a hitters hips, and more importantly his shoulders, to open up early, hindering bat speed and power. Take a look at the progression below:

Devers starts with an open stance in the first frame, pulls his foot in to toe taps (for timing), and then steps back out and plants his foot offline as he swings. What keeping a closed stance does for Devers is allows that toe tap (which he continues to utilize) to take place on the far right side of the box so that when he steps out again, his front foot is more in line with his back – no longer stepping in the bucket.

It’s hard to tell every little detail from the broadcast, partially because David Hess is in the way of Devers’ footing throughout a lot of the swing, but also because the camera is a bit off center, unlike the Pruitt clip. In frame three of the sequence above, it does seem as though Devers is still open a bit, but a good portion of that illusion comes from the off-center nature of the camera. Without seeing his feet exactly, I feel confident that this step/stride/swing is a lot more online than in the past, and it’s largely due to his new, square stance.

I’m not a professional hitting coach in any way. My opinion and analysis of specific swing mechanics is probably not 100% correct. In fact, whatever Martinez and Devers worked on together and the reason for scrapping the closed off stance is perhaps likely not even this.  This is just what I’ve noticed with Devers after news of working with J.D. Martinez surfaced. Maybe this lone home run on Tuesday night will end up being just a coincidental outlier in a season that will continue to be plagued by fastball struggles for Rafael Devers. However maybe, just maybe, JD Martinez and his knowledge of hitting just impacted the Boston Red Sox in a way that you won’t find on the stat sheet, and Rafael Devers can begin to hit better against fastballs.


Photo credit: Kim Klement/USA TODAY Sports

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