When J.D. Martinez joined the Houston Astros as a rookie in 2011, he drove in 28 runs that August alone and was regarded as a hitter with great promise.
But by the following season, MLB pitchers discovered weaknesses in his swing, driving his average down to .241.
Martinez felt aimless until he realized that a teammate, Jason Castro, was crushing major league pitching with a swing that looked . . . strange.
“He asked Castro about his swing and heard about a coach who taught him the mechanics. This coach had never worked as a hitting coach, [or] played professional ball at all,” writes Jared Diamond in his new book, “Swing Kings: The Inside Story of Baseball’s Home Run Revolution” (William Morrow), which looks at the sport’s home-run explosion that climaxed in 2019 with 6,776 homers, demolishing the previous record of 6,105 in 2017.
When Martinez saw a clip of 2011 National League MVP Ryan Braun and noticed he had the same swing, he pressed Castro to connect him with the man who had coached them both. And that’s how Martinez met Craig Wallenbrock.
Born in 1946 in Missouri, Wallenbrock was a promising young hitter who learned the conventional wisdom on how to swing a bat: “Stay back [and] swing down.”
The terms “swing up” and “swing down” refer to whether the bat is on an upward or downward trajectory at the point of contact, when it connects with the ball. The notion that swinging down was the best method is a relic from the game’s early days in the 1850s, when fly balls were called out on one bounce, lessening their value. Despite the likes of Babe Ruth and Ted Williams swinging up, baseball, a conservative sport at heart, found it hard to shake its founding traditions.
Wallenbrock earned a partial scholarship to San Diego State due to stellar fielding, but his hitting declined over time. “It seemed like the higher I went, the more I struggled,” he says in the book.
“I put that to the fact that the competition was getting better, but really, the coaching was getting worse.”
He became disillusioned with baseball during the Vietnam era and became a “pot-smoking hippie.” But he couldn’t shake the feeling that he should have been better.
“I thought I was better, but I wasn’t producing,” he said. “I looked at myself as a failure, that I couldn’t learn to hit.”
In 1971, his younger brother Judd started playing high-school baseball, and Wallenbrock wanted to help him figure out his swing. At the time, Wallenbrock was throwing batting practice for some of his old college teammates who were now playing pro ball, so he brought along a video camera to record their hitting and later reviewed the film with his brother.
“The idea of filming hitters seems obvious now, but back then it was unheard of,” writes Diamond. “Wallenbrock approached the teaching of hitting as an outsider, free of biases and preconceived notions about the ‘right way’ to do it. And what he saw once he started watching made him rethink everything he thought he knew about how to hit.”
Wallenbrock noticed that none of the great hitters swung down, as he and his peers had been taught. Watching video of greats like Hank Aaron, Stan Musial and Ted Williams, he saw that they all swung up. But when he mentioned this to his major league friends, no one believed him — even though some of them did it themselves.
Watching video of the pros, he saw that “the great hitters didn’t propel their bats forward with their top hands, as he had been taught to do. Instead, they kept their barrel behind the ball for as long as possible.
“He called it ‘lag position,’ ” Diamond writes, “and he soon realized it was perhaps the single biggest thing that separated great hitters from everyone else.”
Wallenbrock furthered his knowledge by “studying predators from nature, the big cats and the wolves, to see how they generated so much power.”
He noticed that these predators pounced from their heels. This was a stark contrast to how he was taught to swing the bat while positioned on the balls of his feet.
By the early 80s, he had taken a series of college coaching jobs, eventually becoming the hitting coach at Mt. San Antonio College, a junior college near Los Angeles where major league players trained in the winter. Growing his skills, his contacts and his theories about the swing of the bat there eventually led to scouting jobs with the White Sox, A’s and Indians.
By 1998, having become well-known for independently coaching major leaguers like Michael Young and Brad Fullmer, he paired with an independent coach named Doug Latta at a warehouse facility in Chatsworth, Calif., called the Ball Yard. Wallenbrock rented a batting cage from Latta and impressed him — and much of the baseball world — with his knowledge over time.
“I had never thought about hitting in the terms he described it,” Braun, who worked with Wallenbrock as a high-school student in the early aughts, says in the book. “He was like a mad scientist when it came to hitting, because I hadn’t heard hitting dissected mechanically the way he was able to dissect it.”
When Martinez met Wallenbrock in early 2014, he had one request: “to be taught to swing like Jason Castro.” But after watching Martinez, Wallenbrock told him his swing would require a complete overhaul.
“J.D., I need to remake you,” he said. “Your whole foundation is bad.”
Martinez spent two weeks working with Wallenbrock, learning “not to chop down on the ball but to swing up on it,” Diamond writes.
Thanks to this training, Martinez was reinvented. Having never previously hit more than 11 home runs a season, he hit .315 with 23 home runs for the Tigers in 2014, then exploded the following year with 38 home runs and 102 RBIs. Now on the Red Sox, the three-time All-Star has had two 40+ homer seasons to date.
Now working as a private hitting instructor and a consultant for the Los Angeles Dodgers, Wallenbrock, 73, boasts three former students or proteges currently working as major league batting coaches: the Mariners’ Tim Laker, the Padres’ Johnny Washington, and the Dodgers’ Van Scoyoc.
Wallenbrock’s ingenuity and inventiveness have helped make baseball a home-run bonanza.
“He’s an innovator,” Mariners general manager Jerry Dipoto says in the book. “His ability to teach it, not just to the players but to a series of coaches that have branched off to become something greater, is pretty awesome. It has changed the game.”