2017 has so far been Didi Gregorius' finest season. He's steadily improved with each year that he's been with the Yankees, and in 2017, he's combined above average offense with strong defense at shortstop, one of the most challenging positions on the field. That he was acquired for just pitcher Shane Greene is proving to be a masterstroke from Brian Cashman.
His .312 batting average would be a career-high. His .478 slugging percentage would be a career-high. His 111 wRC+ would be, you guessed it, a career-high. That combination of quality offense and defense has already given him 1.8 fWAR, a total which would put him on pace for 5.5 fWAR per 650 plate appearances.
This kind of production across a full season would make him an obvious All-Star, and someone who could generate down-ballot MVP support in the right year. That was never really supposed to be Gregorius' profile, as he came up through the minors and established himself in the majors as a player who generated plenty of value with the glove but didn't have nearly enough of a bat to be a star.
Which leads one to the matter of the sustainability of his play. Before he returned from injury this year, I wrote that Gregorius would almost certainly have to alter something about his approach at the plate or his batted ball profile if he wanted to produce offensively the way he did in 2016. Instead, he hasn't made any clear alterations to his game and has somehow gotten better.
Yet that makes it all the more likely that he can't keep this up. If there was an obvious change in approach at the plate, a sudden increase in striking the ball with authority, or perhaps evidence that he was a fly ball revolutionary, it would be easier to cast this year as a sustainable breakout for Gregorius. What we're left with in actuality is a player who is reaping rewards for doing essentially all the same things he's done in recent years.
As mentioned earlier, Gregorius is running a career-high slugging, to go along with a .166 ISO and a career-high BABIP (.329). That's a boost in power, a boost that, if accompanied with a subsequent change, would make it plausible to buy into his breakout. Yet his hard hit rate is just 22.5%, down from 24.5% last year and 23.9% for his career per FanGraphs. According to Statcast, just 20% of his batted balls have been struck at 95 mph or harder, one of the lowest rates in the league among regulars. His average exit velocity on air balls (89 mph) puts him in the same range as such noted power hitters as Jacoby Ellsbury, Albert Almora, and Eric Sogard.
A player can boost his power through means other than simply hitting the ball harder, such as trying to hit the ball in the air more. However, Gregorius doesn't profile as someone who's engineered his swing to put the ball in the air in hopes of generating more extra-base hits. His 42.7% groundball rate is up from 40.1% last year and 41.0% on his career. His average launch angle has hardly moved, from 13 degrees in 2016 to 12 degrees in 2017.
There's just nothing about the way that Gregorius hits the ball that indicates he can consistently post a slugging percentage close to .500. Of course, the same could have been said of Gregorius last season, and he's managed to maintain his power so far, but that doesn't mean he's likely to keep it up indefinitely.
This is somewhat troubling given the absence of many other notable offensive tools in Gregorius' skills. His walk rate is at a minuscule 2.8% this year, thanks to a hyper-aggressive plan at the dish. His overall swing rate of 59.1% is the second-highest in the league among batters with at least 200 plate appearances. He's swinging at 43% of pitches he's sees out of the zone, which is a problem, since opposing pitchers are aware of his lack of plate discipline and have thrown pitches in the zone just 40% of the time to Gregorius, well below the league average of 45%.
Gregorius' one saving grace here could be his ability to make contact. Even earlier in his career, when he was earning a reputation as a slick fielder who had very little pop, he at least flashed impressive bat-to-ball skills. Even those have eroded. His contact rate on pitches out of the zone has fallen from 72% last year to 66% this year, and his contact rate on in-zone pitches is down from 91% to 87%. His overall contact rate of 77.6% would be a career-worst.
I think it's pretty easy to speculate that Gregorius has ultimately performed worse at the plate than he did last year, despite his career-best results. In Gregorius, we have a player who is leaning into his extremely aggressive approach, but has lost some of his bat-to-ball skills, without any sort of improvement in his batted ball profile to show for it. If his power suddenly evaporates, Gregorius will be left without any sort of on-base ability to compensate, and the fact that his contact abilities are trending in the wrong direction is another inauspicious sign.
This isn't the end of the world. Gregorius never needed to be a great hitter to be a valuable, exciting, and eminently likable player. Even if he isn't actually a 20-25 home run hitter based on true talent, Gregorius can still get by on the strength of his defense and his ability to avoid strikeouts. But it's too much to ask for this to continue. If Gregorius kept hitting like this, the Yankees would have a star on their hands. There just isn't much reason to believe he will.