It's been a short time in Arizona, but JD Martinez has quickly earned the nickname "Just Dingers". And it couldn't be more fitting after Monday night's game against the Los Angeles Dodgers, where he became the 18th player in MLB history to homer four times in one game. Amazing!
But here's the thing - before Arizona, JD Martinez was a very good hitter. And I don't mean in just hitting lots of dingers. JD Martinez was very much like Paul Goldschmidt - he had one of the highest BABIPs in baseball. From the start of 2014 to July 18th, 2017 (when we acquired JD Martinez), "Just Dingers" had the second-highest BABIP in baseball:
BABIP Leaders, 3/1/14 - 7/18/17
I mentioned it before when I wrote up about JD after his acquisition, but his BABIP skills were actually very special. Despite a 25.8% K%, Martinez was still able to put up a .300/.361/.551 (145 wRC+) line. His walk skills weren't good nor bad, but he was great at hitting for average and elite at hitting for power.
However, his tenure in the desert, so far, has been a bit different:
.255/.333/.678 (146 wRC+)
His overall production has barely changed, but the way he's done it has changed considerably. JD is currently sitting on a .423 ISO and a .241 BABIP. In other words, JD Martinez has been dependent on being "Just Dingers" in AZ.
However, we shouldn't really expect that to continue, going forward.
We can look at his batted ball data to get a quick idea of what's going on here. Let's compare JD during his time in Detroit (2014 - July 28th, 2017) with his time in AZ:
Detroit: 22.0% LD%, 39.0% GB%, 39.0% FB%, 20.7% HR/FB%, 42.9% Hard%
Arizona: 14.9% LD%, 33.7% GB%, 51.5% FB%, 34.6% HR/FB%, 46.5% Hard%
There is actually good news here. But let's start with the bad: we shouldn't expect his 34.6% HR/FB% to continue. Using FanGraphs xHR/FB% calculator, JD Martinez should be around 26.0%. That's still really good, but it's still an obvious spot for regression. And with less homers, JD would see a drop in wRC+.
However, his LD% is also sustainably low. This is eerily similar to early season Goldy, whom had a BABIP below .300 and a rather low batting average (relative to normal). Well, now, Goldy is sitting with a .362 BABIP and 156 wRC+, so the regression was quite nice to him.
We should expect nothing different from JD. We shouldn't expect the low LD% to continue and as a result, his BABIP and batting average should move back up closer to his norms seen in Detroit.
The end picture is that we'll likely see less homers but better average/OBP from JD Martinez. If he keeps hitting the ball as hard as he is currently doing in AZ, his wRC+ might actually increase from 146 despite the drop in homers.
What Else Has Changed?
JD Martinez is also sitting on a 29.2% K%, which is quite a bit higher than his previous norm. This, combined with his drop in BABIP, explain why his batting average has dropped so much since coming to AZ.
I do not expect his K% to stay this high. JD's O-swing% (swing rate at pitches outside the zone) is a bit higher but not drastically. However, his contact rates are quite a bit lower: after averaging about 72.7% in Detroit, JD is sitting at 69.0% in Arizona. Furthermore, JD Martinez is only seeing pitches in the strike zone 40.8% of the time in AZ, compared to 44.3% while in Detroit.
This is speculation, but it seems like JD Martinez might be having to go through some adjustments to the NL pitches he's rarely seen. They're rightfully afraid of him and not throwing him strikes. JD is seeing a nice increase to his BB% this season and hopefully as he continues to adjust to the new league and new pitchers, he'll stop chasing as much and make a bit more contact.
Just Dingers Going Forward?
This has been a pretty simple post to write up but the reality is that we shouldn't expect Just Dingers to only be hitting home runs going forward. JD Martinez's skillset before AZ was very much a slugger, but with much better non-homer batted balls. JD is likely going to shift back to that form. He'll still be a very, very good hitter, but in a bit different way than we've currently seen in AZ.
And, for fun, here's a bonus for JD Martinez: the spray chart for his 4 homers on Monday night.