For ease, we are only looking at the data of what he has seen so far this season (and considering he only played in 8 games in the Majors last year, it wouldn't give us much extra data anyway). Here are the speed and spin of all the pitches he has seen so far this year, labelled with locations:
aller than league average (though we are clearly not working with a large sample size). To get another perspective, the following graph is the release points of the pitchers that have made him whiff so far this season:
It is a pretty diverse group here, with more lefties than righties (no surprise), but some really low righties (which is surprising since he should see that release point better). Here are the opposing pitcher release points on balls Gregorius has put in play (including homers):
The platoon advantage for the left-handed hitter becomes a little more clear here, though he has put balls in play from lefty specialist type release points. Gregorius has 48 whiffs versus 92 balls put in play (including homers, a .52 ratio). League average swinging strike (whiff) percentage is 9.2%, while, from best I can tell, 18.4% of all pitches are put into play (including homers, a .5 ratio). So Gregorius is about league average, maybe a little worse at whiffing versus putting balls in play. Considering he isn't a guy that projects to hit a lot of power, you would like to see a higher ratio, but it isn't alarming yet. First, here is the speed and spin graph for all the pitches Gregorius has "batted", labelled with the fielder who fielded the ball or general direction the ball was hit:
Comparing to the spin and speed chart of his whiffs, we see a greater concentration of below average fastballs. He also seemed to hit more curves than whiff at them, which is a little unusual. He isn't just tapping them either, as many of them are going to the outfield. Not surprisingly, most of the better than average fastballs he has made contact with are going to the opposite field.
The following graphs will break down the pitches Gregorius is hitting for outs, hits, and run scoring plays. Here are the outs:
No giant cluster, but a lot of curveballs put in play for outs and a good number of average and below average fastballs. Here are his hits:
Here we see less curveballs and more fastballs, including a cluster of better than average fastballs, especially ones thrown low in the zone. This seems to support the idea of left-handed hitters liking low and in fastballs. Here are Gregorius' run scoring pitches as designated by GameDay (homers and other RBI plays):
The pattern is clear here, as they are mostly fastballs (with some changeups) thrown in the middle part of the plate. They aren't breaking balls, so he isn't merely a mistake hitter, but his power is coming off pitches that are coming off pitches that catch a lot of the plate.
To continue the look, here are the pitches Gregorius has hit up the middle:
Surprisingly, a lot of breaking balls, with a lot of the pitches overall being pitches that are thrown away, especially up and away that he is just flicking the other way and not trying to pull.
Overall, I think Gregorius is a little more advanced of a hitter than I thought he would be. He isn't flailing at breaking balls or pulling balls he shouldn't. The power he has shown so far is probably mostly a mirage or a product of the ball park and not something I think he will really maintain. You can bust him up and in, which raises some questions either mechanically or bat speed wise. If he doesn't handle inside good fastballs well and all his power is pull, I don't think it is something he will keep up. He seems to be a good low ball hitter and should have success going the other way. If you believe in the defense and athleticism, then it seems that Gregorius is going to do enough at the plate to be a starting shortstop in the big leagues, even if the K/BB might frustrate some.
*I usually Brooks Baseball's Tabular data, but Baseball Savant has made getting spreadsheet data of each player or team very easy, so that is what I used for this post. Keep in mind that the velocities come from the more traditional 50 feet release point than the 55 feet release point Brooks uses, and Drew Willman uses "zones" (which I changed into words for this post) instead of the actual data points for locations.