Didi Gregorius is hitting for power and excelling against lefties

There had always been questions surrounding what Didi Gregorius’s bat would be ever since his earliest days in the minors. He was never expected to hit much at all, and especially not for power. A plus defender at shortstop doesn’t need to hit much, but even then scouts were concerned that he’d end up as a utility infielder. Following in the footsteps of the greatest-hitting shortstop of the live-ball era — to whom his former GM once compared him — only increased the pressure on him.

In his major league career going into 2016, Gregorius hit .253/.316/.368. He has always been good at making contact as evidenced by his 15.9 percent strikeout rate, but his offense was a below-average 86 wRC+. The good news is that his offense was more than enough to keep his plus glove in the lineup last year. Baseball Reference had him worth 3.3 WAR in 2015.

This season, Didi’s batting average has risen 23 points, but because of his decreased walk rate his OBP is roughly the same. The real story is his .168 ISO! His 13 HR have already surpassed his career high of 9 HR, and he is only two doubles away from tying his career high in that category. The home runs aren’t too hard to explain. His hard-hit rate is roughly equal to that of his career, yet his 10.6 percent HR/FB is way higher than his career rate of 5.9 percent going into 2016. Many might assume that Gregorius is taking advantage of that short right field porch at Yankees Stadium, but he has only hit seven of his thirteen home runs there. As for the doubles, he’s gotten 15 of his 22 total at home, so his home stadium might be working in his favor there.

What I have found most interesting about Didi’s season is his huge reverse splits. He is hitting an excellent .344/.388/.479 against LHP and a disappointing 268/.292/.438 against RHP. When it comes to analyzing platoon splits, it’s best to use weighted on-base average, so to reiterate Didi’s splits, he has a .376 wOBA against LHP and a .309 wOBA against RHP. For his career, he has a .281 wOBA against LHP and a .317 wOBA against RHP. He is only slightly worse against right-handed pitching but worlds better against left-handed pitching this season. So does this mean that Gregorius has figured something out against lefties? Should opposing managers have a right-handed pitcher face him in high leverage situations?

Absolutely not. In-season platoon splits have no predictive value because they suffer from small sample sizes. In the case of Gregorius, it’s only 105 PA spread out over four months. Furthermore, as demonstrated in research presented in The Book, no hitter has true-talent reverse splits, and a left-handed hitter needs at least 1,000 PA against left-handed pitching for his actual splits to represent his true talent.

To determine Didi’s true talent splits, we have to take his career splits and regress them heavily toward the mean splits for left-handed hitters. If you’re interested in a primer on how to do this, I suggest checking out this post by Matt Klaassen at FanGraphs.

The easiest way to do this is to download this calculator made by Ian Malinowski. Since it’s a little out of date, I had to update the splits percentage. I calculated the average platoon split for left-handed hitters going back to 2014 at 8.3 percent. This means that left-handed hitters were 8.3 percent better against right-handed pitching as opposed to left-handed pitching. Plugging the numbers into the formula tells us that Gregorius has a true-talent .320 wOBA against lefties and a .281 wOBA against righties, which is a 10.5 percent split. Not only does he not have real reverse splits, his projected splits are a bit larger than the average left-handed hitter. The good news is that they are smaller than his actual splits of 11.7 percent.

A .356 BABIP appears to be the main culprit for Didi’s success against left-handed pitching this season. He also has a 14.3 percent infield hit rate against southpaws versus 9.4 percent for his career.

That doesn’t necessarily mean that there’s zero progress, though. Obviously, hitters can improve how they hit same-sided pitchers and reduce their platoon split. Let’s take a look at Didi’s exit velocities the last two seasons courtesy of Baseball Savant.

Baseball Savant

Baseball Savant

As you can see, Gregorius is hitting the ball harder against left-handed pitchers this season. Unfortunately, we don’t know enough about exit velocity yet to conclude that he’ll continue hitting the ball that hard against lefties. What we can conclude from this data and his regressed platoon splits is that Didi has likely improved against left-handed pitching. As a 26-year-old in his fourth full season who was never shielded from left-handed pitching, he was bound to improve eventually. He’ll likely continue to do so.