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…