One Big Question: Can J.D. Martinez rebound against righties?

Welcome to Over the Monster’s One Big Question series. For those unfamiliar, this is something of a season roster preview where over the next 40(ish) (week)days we’ll be taking a look at each player on the 40-man roster prior to the season. If changes are made to the roster between now and Opening Day, we’ll cover the newly added players. Rather than previewing what to expect in a general sense, the goal of this series is to find one singular question — sometimes specific, other times more general — for each player heading into the coming season. We’ll go alphabetically one by one straight down the roster, and you can catch up with the series here. Today, we cover J.D. Martinez.

The Question: Will J.D. Martinez terrorize right-handed pitching again in 2020?

In the grand scheme of things, on a normal scale with which we would judge a normal baseball player, J.D. Martinez was a very, very good hitter in 2019. If you polled major-league hitters all across baseball, almost all of them would look at what the slugger did last year and call it a success. He played in 146 games and he hit .304/.383/.557 for a 139 wRC+, the latter mark coming in at number 16 in all of baseball. It seems wild to call him disappointing. I probably wouldn’t go so far to say that, but he probably did come in at least a bit below expectations. That 139 wRC+ was his lowest since 2015 and it was a whopping 31 points below where he finished in 2018, his first season in Boston.

Consider that in the two seasons before last, one of which was in Boston and the other split between Detroit and Arizona, he finished wRC+’s of 170 and 167, respectively, as well as Isolated Powers (SLG - AVG) of .387 and .299. Last year his power dropped down to a .252 ISO, which doesn’t seem like that big of a drop until you remember the state of the literal baseball. Is it unfair to expect 2017/2018 performances from Martinez every year, especially as he gets set to start his age-32 season? Perhaps. But we know he’s capable of doing it again, and with Mookie Betts no longer in the lineup it sure would be helpful if he got back to that point.

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If he is to get back to the point, the easiest path for him to get there is to go back to destroying right-handed pitching. Martinez was, as always, a beast against lefties last year, putting up a 242 wRC+. Against righties, though, he was merely average, finishing with a 103 wRC+. Compare that to how he finished 2018 (175) and 2017 (147) and it’s clear this is the big differentiator between the seasons.

As I was trying to figure out what happened, my first thought was that he was just hitting too many balls on the ground. According to FanGraphs, he hit the ball on the ground 46 percent of the time against righties last year compared to a rate of just 33 percent against southpaws. However, upon further review that’s actually a difference of only two percentage points from 2018 and four percentage points from 2017. That’s not literally nothing, but it’s not enough for him to crash down to average offensive levels.

My next hypothesis was that right-handed opponents must have approached him differently as they were sick of being owned on a nightly basis. That also turned out to be true, as the rate at which he was seeing different pitch types stayed roughly the same (per Baseball Savant’s tracking), as was the rate at which he was seeing pitches in various areas of the strike zone.

What did change, as I eventually discovered, was his performance against fastball. This wasn’t the only change, but it was certainly the biggest. In fact, it was big enough that it played a role in his overall numbers. By FanGraphs pitch value metrics, which measures how well hitters do against different pitches, Martinez about 17 runs against fastballs, which is good but is also a drop from 40 in 2018 and 27 in 2017. Looking at Baseball Savant, though, it becomes clear that this is entirely against righties, as against lefties he actually improved his whiff rate, expected wOBA and actual wOBA against fastballs. However, against righties the latter two numbers fell to .397 and and .360, respectively. These are good marks, to be fair, but they’re also significant drops from 2018 (.473, .481) and 2017 (.499, .477).

There’s a couple of zone plots that stood out to me as I tried to dig deeper into this. For the purposes of brevity and page cleanliness, I’m going to take 2017 out of the occasion and just focus on comparing Martinez’ two seasons in Boston. First, I want to look at the rate at which he swung at pitches in different spots on the zone.

It stands out to me how much less often he swung at pitches all across the top of the strike zone, particularly when the trend continues out of the zone only on the inner half. If you recall some of Martinez’ biggest hits in his first year in Boston, it was on the high fastball. Which brings us to the my other plot comparison which looks at the average exit velocity from different points in the zone.

Here, Martinez does just about as well on the pitches up in the zone that are middle or inside, but there is a major difference up and away that happens both in the zone and out of it. This is a major issue for Martinez, who as we all know is at his best when he is driving a fastball up and away and crushing it to the opposite field. There aren’t many, if any, better hitters in baseball at doing just that. Sure enough, according to FanGraphs, Martinez’s ISO was just .167 against righties when he went the other way in 2019. In his previous five seasons, dating back to his initial breakout with Detroit, his ISOs in those situations were: ..378, .250, .333, .333, and .256. I should of course note we’re dealing with a small sample here — just 90 batted balls last year — but the trends all point to an issue with fastballs up and away that takes away perhaps the most valuable part of Martinez’s tool chest at the plate.

I have very little doubt that Martinez is going to be a productive hitter in 2020, which he managed to be in 2019 even while being average against righties. He has been one of the best hitters in baseball for six years running now and has earned the benefit of the doubt until he proves otherwise. That said, if he wants to be out-of-this-world elite again, he needs to be better against righties, and specifically on fastball up in the zone against righties. I don’t know if this was a fluke or a mechanical issue or a side effect of his back problems that were on and off all year or some combination of all three, but it held him back in 2020. The Red Sox need the best version of Martinez to boost their offense to another level without Mookie Betts, and this is the path to get back to that point.