Didi Gregorius has reversed his platoon split, but what does it mean?

Didi Gregorius hasn't had the greatest start to the season, hitting .276/.298/.400 with an 89 wRC+. That's not to say he's been awful, especially given his excellent-as-always defense, but an on base percentage under .300 just isn't going to cut it, especially when there's not much power or speed to go with it. Gregorius has also seen his hard contact rate plummet to a painfully bad 13.8%, second worst in baseball. His average exit velocity of 86.1 mph is 11^th worst in the league and he has done little on the base paths. Overall, early returns have been disappointing compared to Gregorius' strong finish to 2015.

This is starting to feel like the beginning of a "What's wrong with Didi Gregorius?" piece, but I want to focus on something a bit more unique. As I was wading through the uninspiring numbers of Gregorius' 2016 season, I came across a statistic that may not get the blood flowing in the average baseball fan, but that I think is pretty cool. It's something that Gregorius has done this season that is extremely out of the ordinary. No, it isn't his five walks in 43 games, though that is noteworthy in and of itself. What caught my eye is Gregorius' complete reversal of the traditional platoon split.

When the Yankees acquired Gregorius in the 2015 offseason, the general consensus was that he would begin the season in a platoon, only receiving at bats against right handed pitchers. This made sense, considering he hit .137 against southpaws in 2014 and .200 the year before. Like most left handed hitters, Gregorius had a considerable difference in production against RHP vs. LHP. Gregorius improved this split last season, but it still clearly remained. This season, he ripped any semblance of a normal platoon split to pieces, and then some.

The most remarkable part of Gregorius' transformation is undoubtedly his newfound success against lefties, upping his wRC+ from 73 in 2015 to 133 this year. Gregorius himself attributed this to "just trying to see the ball better and not letting my front shoulder fly open," and that's manifested itself in his batted ball profile. An area of focus for Gregorius appears to be going the opposite way, as he's increased his oppo% from 15.8% in 2014 all the way up to 37.5% this year. That strategy makes sense, as Gregorius isn't great on the outside of the plate, and it appears to have paid off.

Gregorius is also whiffing less and hitting the ball much harder, increasing his exit velocity from 83.9 mph last year to 89.21 mph. He's been hitting fourseamers and sliders better as well. It's hard to explain exactly why, suddenly, everything is working for Gregorius against lefties, though he deserves a lot of credit for improvements.

Even with a huge boost in production against southpaws, Gregorius still has a mere 89 wRC+ this season. That's because he's no longer hitting righties as well as he used to, giving up a distinct reverse platoon. Considering he faces right handed pitching much more often that lefties, this isn't great news. It's unlikely that his success against lefties is responsible for his struggles against lefties, though it has created the unique split he has this season.

Fastballs have been a big reason for his issues with right handed pitching. Against righties last season, he hit hard stuff very well. This season...not so much. The two most notable changes were against the four-seam fastball and sinker, or in other words, the two pitches he's seen most often this year. A .267 batting average against the four-seamer wasn't great, but it sure is better than the .211 mark he carries now. The drop from a .352 average to .273 on the sinker has also been a big blow for Gregorius. He has seen his swing rate on fastballs go up on pitches high in the zone and on the inside corner, which is unfortunate considering he's never had much success against fastballs in those locations. Although swinging more in areas where he never gets hits isn't the greatest plan for Gregorius, it's a fixable problem.

It's probably more correlation than causation when it comes to Gregorius' new success against lefties and struggles against righties, but the change in his platoon split is awfully interesting. It's not often that a left handed hitter like Gregorius makes such big strides against lefties, and the improvements he's made really are astonishing. He hasn't yet seen an overall boost in performance because of issues against the opposite hand, though there's a good chance he's able to improve in that facet of the game. It's been a lackluster season for Gregorius thus far, but things should improve once he starts to hit righties again. This new platoon split isn't going to last forever given unsustainable performance on both ends, but he will come out of this season with less of a split than ever before, and that is a vital development for Gregorius.