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Hot streaks and J.D. Martinez

What happened in September? A look back.

MLB: Miami Marlins at Arizona Diamondbacks Joe Camporeale-USA TODAY Sports

This past September, Arizona Diamondbacks rental J.D. Martinez erupted in a pillar of fire. In 106 plate appearances, he blasted 16 home runs, posting a .396/.434/.950(!) line, working out to a 242 wRC+.

By OPS it’s the 13th greatest September a player has had since 1901. It was vital to the Diamondbacks snagging home-field advantage in the Wild Card Game. It was amazing, a seemingly never ending onslaught. Hot months happen for one reason or another, but this could be a fun chance to use Martinez as a case study to see if it stood out at all. Did he do anything particularly different?

Entering September, Martinez was already having a good year because he’s already a good hitter. His slash line was .275/.361/.610 (144 wRC+) even after a particularly sluggish August that saw him put up his lowest OPS by month of the season, a still respectable .873. By all accounts, it was another excellent season in this mid-career leap he’s experienced. His rate stats and counting numbers were pretty much in line with what he’s put up the last few years, and while the D-Back might have been a bit disappointed to that point because his worst month happened to come right when he joined the team, he was still effective.

Then he got hotter than Phoenix in July! By the looks of it, he also got more aggressive at the plate:

J.D Martinez Plate Discipline and Hard Hit Rate

Split K% BB% Hard Hit %
Split K% BB% Hard Hit %
May-Aug 25.8 12.1 45.8
September 27.5 6.4 59.7

This is somewhat instructive; in September, Martinez struck out more, walked less, and hit the ball hard more often than he had previously. At a glance it looks like he was selling out for power, walks and Ks be damned, but if we look at how often he swung, we can really judge his aggressiveness.

Brooks Baseball tracks this though. This chart shows Martinez’s swing rate:

It’s nothing particularly demonstrable, though as this accompanying chart shows, he was missing on breaking balls more than ever in September:

By itself, this isn’t that instructive, other than to say breaking pitches are hard and a lot of the teams in the NL West (Dodgers and Rockies in particular) have pitching staffs with great breaking balls.

Luckily, we have more information! tells us that while Martinez was seeing the same rate of four-seamers he had pre-September, he was also being offered more sliders than ever before. There are a lot of slider throwers in the NL West. But he ALSO was swinging at more of those fastballs than he had all year.

Take a look:

J.D. Martinez vs. Four-Seamers and Sliders

Pitch type Pre-Sept Pitch% Sept. Pitch% Pre-Sept. Swing % Sept. Swing% Pre Sept. Whiff% Sept. Whiff%
Pitch type Pre-Sept Pitch% Sept. Pitch% Pre-Sept. Swing % Sept. Swing% Pre Sept. Whiff% Sept. Whiff%
Fastball 31.7 30.7 47.8 54.3 11.2 15.0
Slider 21.2 28.0 55.7 53.4 20.8 13.3

Martinez likes fastballs. Everyone does of course, but he posted an absurd .522 wOBA against them in 2017, far and away his highest rate. It’s higher than Aaron Judge(.476), Paul Goldschmidt(.471), or Giancarlo Stanton(.465).

It looks like JDM was fastball hunting, and got fooled by sliders because they look a lot like fastballs, until the last instant. In that hunting, he pressed a bit, which led to a drop in walks and a related spike in strikeouts. Supporting this is the fact that just in general, he swung at pitches in the zone more often. In an interview with Eno Sarris, he noted that he focuses on contact rate in the zone - he hates missing strikes. During his locked in month, he was definitely attacking more, especially in the zone:

Again we stand near the problem of sample size, but a month isn’t too small a piece of a season. It is literally a sixth of the season. It seems like he just had a great sense of the zone in September, more-so than the rest of the year, and that he punished pitches he identified.

One last piece of the puzzle, StatCast lets us see how he was striking the ball. It turns out that, in September, he hit the ball harder on average, further, and at a slightly higher angle:

J.D. Martinez StatCast Numbers

Split Exit Speed(mph) Avg. Distance(ft) Launch Angle(deg)
Split Exit Speed(mph) Avg. Distance(ft) Launch Angle(deg)
Pre-September 90.0 203 16.0
September 93.2 217 15.5

I would’t put much stock in the launch angle change considering it’s half degree. But an extra 15 feet of travel on average, and 3 more miles per hour on his exit velocity? That’s something that can’t be waved away by pointing to atmospheric conditions in Arizona. After all, he did spend half the month in Kansas City, San Francisco and San Diego in the early fall. Was he simply swinging harder, and happened to get lucky on seeing enough fastballs in the zone to make this kind of absurd difference? Pitchers do get tired late in the season, and facing guys playing out the string probably helps some.

Martinez probably won’t hit 96 home runs in 2018 as an extrapolated September would suggest. Maybe if he signs with the Rockies he could push towards 60 or 70 with

another month like this past September, but some dreams don’t come true. This hyper-aggressiveness isn’t a long-term solution, but I can’t help but wonder if there isn’t some mental part here, a hyperfocus that simply isn’t possible for a whole season because you’d simply break down.

This was Martinez’s first chance to contend since 2014, his debut season with the Tigers when they were swept in the ALDS by the Orioles. Every player wants to play in October, and he wanted to make sure he got to, as well.

We have no way of measuring it of course, but I still believe players have a way of locking themselves in, having the mental part, the preparation and the physical all mesh at the same time. Maybe it happens by accident, maybe some perhaps are better than others. He changed his approach markedly and mashed. You have to wonder if front offices see this, have some way of measuring it in their own proprietary ways. The psychology of the game is still uncharted territory, much more qualitative than quantitative so it’s hard to, well, quantify.

Undeniable, something happened with Martinez in September. Maybe it was in fact luck. Maybe it was mental, maximizing his ability for a couple weeks. Maybe he just happens to mash all the time, and everything went right. We may never actually know, but it can’t hurt to investigate.

Merritt Rohlfing writes exhaustively at Beyond the Box Score about all things baseball, and does the same thing a bit more often at Let’s Go Tribe, but about the Indians. Listen to his podcast, Mostly Baseball, now on iTunes. Follow him on Twitter @MerrillLunch.