J.D. Martinez Makes History, Keeps Improving

There have been 23 perfect games in major-league history but only 18 four-homer games.

While we’d expect to see the quantity of the latter increase during a home-run spike like the one baseball is currently experiencing, the four-homer game remains one of the rarest individual, single-game achievements of which a player is capable. Perhaps the only rarer deeds are the 20-strikeout game (accomplished five times) and unassisted triple play (recorded 15 times in major-league history).

J.D. Martinez, as you’re probably aware, became the 18th player to produce a four-homer game this Monday. He became just the third one to reach the mark against four different pitchers.

Only six players have hit four homers in a game since the start of the 21st century. Mike Cameron (May 2, 2002), Shawn Green (May 23, 2002), Carlos Delgado (Sept. 25, 2003), Josh Hamilton (May 8, 2012), and Scooter Gennett (June 6 of this year) represent the other five. While Gennett is the unlikeliest player in the modern era to accomplish the feat, Martinez is also an unlikely candidate — if you account for the unusual path he’s taken to stardom.

More immediately, the four-homer game renders even more puzzling the lack of interest in Martinez’s services at the deadline — and, perhaps, helps his case en route to the free-agent market, hinting that this is a hitter who’s still improving.

His 155 wRC+ entering play Tuesday would be a career-best mark, bettering the 154 wRC+ of his breakout season in 2014, the first year following his arrival in Detroit from Houston. At the start of that season, his major-league career was in jeopardy. His struggles had compelled him to search for a new swing.

The search was fruitful. Not only has Martinez established himself as an elite power hitter, but he’s become one of the founding fathers of the modern air-ball movement in the 21st century. He offered some spicy thoughts on swing philosophy and conventional coaching when I caught up with him this spring in the Joker Marchant Stadium clubhouse in Lakeland, Fla.

“You still talk to coaches. ‘Oh, you want a line drive right up the middle. Right off the back of the [L-screen in batting practice].’ OK, well that’s a fucking single,'” Martinez told FanGraphs. “To me, the numbers don’t lie. The balls in the air play more.”

I don’t think there’s anyone doubting his philosophy today.

What’s interesting about Martinez is that, even though he changed his approach and worked with non-conventional instructors outside the game, he never really became an extreme fly-ball hitter. He didn’t make the sort of dramatic changes that Marlon Byrd or Daniel Murphy did in terms of batted-ball distribution. His average launch angle is actually down, to 14.9 degrees, from his 16-degree mark in 2015. This is only the second season during which he’s produced more fly balls than ground balls in his major-league career.

What did change, what did allow him to become a star-level hitter — as subjective as the measure may be — is his hard-hit rate, which is at a career-best level this season.

While hard-hit rate is imperfect, it passes the eye test with Martinez. It also lines up with the Statcast data we’ve had since 2015.

A better measure of the quality of contact is his expected wOBA (.398), the top mark he’s posted, up slightly from his .395 mark last year and from .391 in 2015. He’s fifth in baseball in “barrels” per batted-ball event (16.9%) among qualified hitters; he was also fifth in 2015 (17.6%), 18th in 2016 (14.6%).

By whatever measure you prefer, Martinez is barreling up pitches like few others this year. That trend continued Monday.

One question regarding Martinez as the began season was whether he’d adjust to any collective countermeasures from the league’s pitchers. There seemed to be a case for getting above the plane of his swing with high-spin four-seam fastballs.

But the percentage of four-seam fastballs seen by Martinez has actually dropped this season, from 34.3% a year ago to 30.2% this season. The average height of pitches has also declined, from 2.29 feet to 2.26 feet. And even if he were facing more four-seamers up in the zone, Martinez has improved his ability to damage pitches up there.

Consider his isolated slugging per pitch between 2014 and -16:

And from this season:

Martinez is crushing pitches everywhere.

He’s become more disciplined, his out-of-zone swing rate having declined for four straight seasons and currently sitting at a career-low 31.6% mark. His walk rate is at a career high (11.9%), while his strikeouts remain in line with his career average (25.8%) — even as the league-average rate has increased by a few points.

Martinez is improving — has never been better, in fact — and he put an exclamation point on that Monday night. There might be some contending clubs kicking themselves for not making more of a push to acquire him, and it will be interesting to see what kind of offers await Martinez this offseason. But before then, he’s hoping to help the Diamondbacks play well into the fall.