Kevin Pillar is having a rough season at the plate. His 84 wRC+ is just slightly above last year's mark, when injuries completely sapped his power in the second half. It's even more glaring considering that for the first quarter of the season, he was the team's best hitter. For a couple of months his bat was a black hole before showing signs of breaking out the last week, but the truth is he deserved much better.
We can divide Pillar's 2017 season into three different parts (note: these ranges are in fact cherry picked to magnify the sharpness of the divide for illustrative purposes).
It's been forgotten given what followed, but Pillar actually started the year in a short funk. Over the first three series, he hit .241/.267/.241 (34 wRC+) in 30 trips to the plate. He didn't strike out and walked once, so this lack of production a result of batted balls, and he posted a very low .241 BABIP. But this not "luck", it was earned. Using the headline batted ball data from FanGraphs, he wasn't hitting line drives (14%), hitting a ton of ground balls (55%) and when he got the ball in the air it was without authority (33% popup rate, or roughly 10% overall).
Then Pillar caught fire. From April 13th through May 16th (the game before the one that earned him the suspension), he hit .328/.385/.567 in 149 plate appearances, good for a 152 wRC+. He was walking at a solid clip (8%), striking out at his normal rate (16%), and hit 6 home runs and 19 extra hits in total. A .362 BABIP also certainly helped.
Since then, it's been a long struggle. From May 17th through July 29th (until his recent uptick began), Pillar hit .191/.238/.313 in 245 PA, which works out to an abysmal 42 wRC+. His walk rate went backwards to 4.5%, and he still struck out 16% of the time, so the bulk is on balls in play. Pillar's power went backward, though 5 home runs and 18 extra base hits is actually not bad for him, but the big culprit was a .211 BABIP.
With a .211 BABIP over more than two months, one would assume he was making really bad contact, like at the beginning of the season. But what's remarkable is looking at the batted ball breakdown between his hot part of the season and his long struggle:
If I didn't label them, could you even tell which was the one when he had .362 BABIP and when he had a .211 BABIP? I couldn't, at least with any amount of conviction. He's maintained a strong and essentially unchanged line drive rate, with a few more ground balls at the expense of fly balls (which should help BABIP a little at the expense of power).
Granted, this data is not perfect (batted balls fall more along of a continuum than into buckets, not all line drives are created equal, etc) but directionally it's usually correct. But we have a better tool now, which is Statcast data. And the good folks at MLB.com have done a lot of good work at predicting the hit likelihood for batted balls based on exit velocity and launch angle. So I pulled Pillar's data and broke it into the time periods above:
Since this includes home runs, I'm not using BABIP anymore. We see the poor contact at the beginning of the season reflected in a lower expected average. We see that he got some "luck" in the middle (this is likely related to my cherry picking the time period based on results), but he definitely was crushing the ball and earning most of it (this shows up more on the power side than the batting average side).
But the last couple months? The batted ball quality suggests he should be a little below average (average BABIP is around .300, but adding back home runs moves it higher), but nothing close to what he's actually achieved. Pillar is "missing" about one in every four hits he should have earned over the past couple months.
It's not nearly drastic at the season level, since it's offset to a significant degree by overshooting in the first stretch. But it's still cost him about 16 points of wOBA on batted balls, or around 12 points overall, which would otherwise have his wRC+ in the 92-93 range.
So, as bad as the last couple months have been for Pillar, the good news is the underlying numbers have been fine. He's always going to have hot and cold stretches because his results are so geared to the results of balls in play, but there's no evidence that his ability has been fundamentally impaired.