After putting up ridiculous first-half hitting numbers (162 wRC+ over 351 plate appearances), Matt Carpenter was named to the National League All Star roster — the lone St. Louis Cardinals representative — for the third time in four seasons. Unfortunately, due to an oblique injury suffered during a check swing on July 6th against the Pittsburgh Pirates, Carpenter was unable to participate in the game and was replaced by deserving rookie teammate Aledmys Diaz. After spending one month on the disabled list, Carpenter returned to live action on August 5th, but as he fought through the recovery of a notoriously nagging injury, he simply was not the same hitter the rest of the season.
Matt Carpenter Hitting, Pre- vs. Post-Injury
Pitches per plate appearance
Prior to the oblique injury, Carpenter was facing 4.268 pitches per plate appearance. Upon return, this number dropped to 4.126. On the surface, the difference does not seem like much, but when you project it over 664 plate appearances — Carpenter’s average over the last four seasons — the difference equates to ~94 pitches — of which could provide Carpenter with more than a handful of opportunities to do some damage.
A contributing factor to the aforementioned decrease in pitches per plate appearance was Carpenter’s post-injury increased swing rate on pitches out of the strike zone. Prior to injuring his oblique, Carpenter faced 919 pitches out of the strike zone and swung at 24.9% of them. After returning to the lineup, Carpenter swung at 26.9% of the 565 out-of-the-strike-zone pitches he faced. While a post-injury 10.7% walk rate is still above league average, it was well below both his pre-injury and career rates. Swinging at pitches out of the strike zone definitely played a role in this decline, which subsequently helped lead to a more-than-100 point drop in on-base percentage.
So, were pitchers approaching Carpenter differently, post-injury?
While the heatmap “core” (dark brown spot) shifted outward one deviation post-injury, pitchers’ general approach to Carpenter stayed pretty much the same. If anything, in the process of attacking him down and away, they strayed toward the lower middle part of the zone more frequently upon his return from the oblique strain (as you can see by the kickout to the right of the screen, forming a bean-like resemblance). This stray pattern is important to note considering Carpenter historically rakes against pitches down, but in-the-zone pitches.
Launch angle comparison
In all honesty, launch angle is where the story is told. Of course, you could always look at the “old school” pre- and post-injury line drive rates — 27.2% and 24.6%, respectively — but the batted ball difference is even more evident when viewed as a side-by-side launch angle comparison. As you may recall, the desired launch angle ranges from 10 to 25 degrees, or what is more commonly classified as a line drive.
Well, as you can see in the diagram on the left, pre-injury Carpenter was consistently batting balls within the desired launch angle range. In fact, his four highest peaks all took place within the desired 10 to 25 degree range, with 20 degrees being his most frequent destination. On the other hand, post-injury Carpenter was considerably less consistent with launch angle. That desirable 20 degree launch angle all but disappeared. In addition, he had a dramatic shift in batted balls skyward to the 35 degree launch angle, which may work out okay for a home run hitter, but not for a hitter of Carpenter’s stlye. Heck, he was even pounding more pitches into the ground than he was prior to his disabled list stint, which again highlights his inconsistent post-injury launch angles.
Spray chart comparison
For good measure, I decided to include a side-by-side spray chart comparison as well. Given the amount of data points, it isn’t always easy to discern anything from spray charts, but in Carpenter’s case, one difference stands out in particular. Notice the relative absence of yellow dots (line drives) up the middle in the spray chart on the right (post-injury)? Based on what we saw in the launch angle comparison, this isn’t all that surprising, but it is important to note that during arguably Carpenter’s best offensive half season, he was consistently driving liners up through the middle of the field.
No, I do not have a miracle fix for Matt Carpenter in 2017. Frankly, I don’t think he really needs one, either. Instead, I think after an extended offseason of fully recovery (and rehabilitation), the former(?) leadoff hitter will finally put the oblique injury behind him and return to the type of hitter we have grown accustomed to over the years. And for those worried about his expansion of the strike zone post-injury? I think that was largely a compensation mechanism associated with lingering effects from the oblique strain and growing frustration due to below-average results. I expect Carpenter to be Carpenter in 2017, and hopefully his home will be the second spot of the lineup, immediately following Dexter Fowler.