The evolution of J.D. Martinez’s plate discipline

J.D. Martinez isn’t just a power bat

Featured image courtesy of (Sept. 23, 2017 – Source: Christian Petersen/Getty Images North America)

If you don’t sleep under a rock, you should have heard by now the Red Sox and J.D. Martinez agreed to a five-year, $110 million deal Monday night.

Naturally, I’ve been scouring Martinez’s various statistic pages for the past, let’s call it 30 minutes to make it appear like I have more of a life than I actually do. I was searching for a different angle, something unique about his statistical profile that I could explore more in-depth. Surprisingly, I found something fairly simplistic that I had not heard anyone really touch on to this point. For the past couple of years, the right-handed power hitter has slowly but surely transformed his discipline at the plate.

Now, before I begin I have to note something: to make sure my work was going to be somewhat original I looked up the words “J.D. Martinez plate discipline” on Google to see if anything of merit came up. Wouldn’t you know Matt Collins of Over the Monster beat me to the punch, talking about sort of the same thing I am going to talk about. Check out his piece, titled “J.D. Martinez is not just a power bat,” here.

In Collins’ piece, he delved into Martinez’s increased BB% (walk percentage), as the source of his augmented sense of plate discipline. While this is entirely true, I am going to expand on what is driving this growth in walk percentage. Before I do, though, this graph, courtesy of Fangraphs, is kind of important.

chart (2)

The renowned transformation of Martinez’s career, where he went from a negative contributor to one of the best hitters in baseball, happened in his first season with the Detroit Tigers in 2014. Ever since that year, he has gradually increased his walk rate, leading to a career-high in BB% at 10.8% last season. As you can see, Martinez was comfortably above-average at drawing free bases in 2017.

On the surface, this can be chalked up to the convenient narrative that pitchers feared him more and therefore pitched outside of the zone more frequently. That is probably true! Actually, it can be confirmed with his career-low — outside of his partial 2011 season with the Houston Astros — 43.6% of pitches thrown within the strike zone in ’17.

With that said, that does not paint the entire picture. The fact of the matter is the newest member of the Red Sox was much more selective chasing pitches last season.

In 2017, JDM only swung at 32.1% of pitches outside the zone. The word only is used relative to himself, as that number is pretty far above average compared to the league-average 29.9 O-Swing% the same year. Against himself, though, he was more selective with pitches outside the zone, which are presumably bad pitches to hit, than in any other season since 2012. Below are his O-Swing%, per Fangraphs, since joining the Tigers:

J.D. Martinez’s O-Swing% 

2014: 36.8% 

2015: 35.5% 

2016: 33.2% 

2017: 32.8% 

This is certainly an encouraging trend. He may have hit for more power than ever before last year but he also was at his peak in terms of plate discipline. Consequently, he also had a five-year low in Swing% at 51.4. It is also worth noting his percentage of pitches swung at within the zone (Z-Swing%) was pretty much aligned with the numbers he posted since transformed J.D. Martinez was a thing.

In terms of aging, relying on power is harder to sustain than plate discipline. The fact Martinez has basically gotten better every single year in swinging at better pitches, without sacrificing his power production, is an extreme positive going forward.

It will be obvious to celebrate the moonshots Martinez will inevitably hit for Boston this year. Just remember to cheer for the free passes he draws, as well. It is a very good sign for him.



Patrick Green

Founder and owner of Red Sox Unfiltered. Communications major at UNCC.

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