Craig Wallenbrock admits he was a poor hitter. He was good enough to play at Pasadena City College, then San Diego State, but before long he was spending more time tossing batting practice than playing in games. “I saw the writing on the wall,” Wallenbrock said. He lasted less than one year on the Aztecs’ baseball team.

Wallenbrock is not a poor coach. As a private instructor, he’s worked with dozens of professional hitters since he began giving lessons out of an industrial facility in Chatsworth. Remarkably, three of his former pupils – Robert Van Scoyoc (Dodgers), Johnny Washington (Padres) and Tim Laker (Mariners) – were named major league hitting coaches in the past month. A fourth, Brant Brown, was recently named the Dodgers’ “hitting strategist,” effectively a collaborator with Van Scoyoc on the team’s major league staff.

At 72 years old, having played and scouted and coached and seen just about everything baseball has to offer, Wallenbrock has sprouted perhaps the fastest-growing coaching tree in any sport. He did not see this writing on the wall.

“It seems like a short span of time,” Wallenbrock said, “but it’s been a long time and it’s suddenly hit at the same time, is kind of how I look at it. I’m probably like a proud father seeing his sons have success. It’s great that the organizations did that.”

That’s easy to say now.

Not long ago, the idea of hiring a private hitting instructor on a major league coaching staff would have been controversial, even taboo. The Miami Marlins made Barry Bonds their hitting coach for the 2016 season. Edgar Martinez preceded Laker as the Seattle Mariners’ hitting coach. A Hall of Fame-worthy playing career has been a sterling prerequisite for coaching major league hitters for most of baseball history. Van Scoyoc never played beyond Cuesta College.

Andrew Friedman, the Dodgers’ president of baseball operations, knew he would be bumping against this tradition when he hired Van Scoyoc.

“I think the fact that he had spent multiple years here (as a consultant), had connected with a lot of our guys, I think those relationships help,” Friedman said. “He’s worked with so many hitters throughout baseball. A number of our guys got texts from players on other teams telling them how lucky they were. It helped them buy in.”

Widespread buy-in from major league teams is a recent phenomenon, yet players have been training with private hitting instructors for years.

Doug Latta opened The Ballyard, his private facility in Chatsworth, some 20 years ago. Wallenbrock recalled scouting Latta at Cal Lutheran University; when he decided to go out on his own as a private instructor, he approached Latta about teaming up. They worked together until 2013, Latta said. Their reputation grew mostly by word of mouth, with little publicity or support from major league teams.

“Having Craig there, immediately we had this high-level clientele,” Latta said. “He’s one of the best in the business. Spending a lot of time right there … it was like being in a doctorate program.”

Wallenbrock’s methods are common practice now. In the social media era, anyone with an Instagram or Twitter account can produce side-by-side videos to compare two hitters and break down their swings. A good coach can even point out why one hitter’s mechanics are superior to another’s. These are among the methods Wallenbrock passed down to Van Scoyoc, Laker, Washington, Brown, and the other pupils in his coaching tree.

In the mid-1970s, these methods weren’t available when Wallenbrock’s younger brother, Judd, first asked him for help making his high school team. Suddenly Craig Wallenbrock had his first pupil. So he did what came naturally: He threw batting practice.

To offer better feedback, Wallenbrock realized he needed a frame of reference.

There was no internet back then, so “we started buying videos of hitters,” Wallenbrock said. “The next thing you know, I started comparing (Judd) with them. That led to doing it with pro players and other people. I just kept up with the technology. If you talk to (Van Scoyoc), I didn’t – he had to help me, which is probably more true. We started doing the video and found it helpful.”

Hitters found it helpful, too. By the mid-2000s, Wallenbrock wasn’t the only coach breaking down video. He’d just been doing it longer than most of his peers, even some who had full-time major league jobs.

Greg Walker, the Chicago White Sox hitting coach from 2003-11, was among the first major league coaches to regularly recommend his hitters to Wallenbrock in the offseason. One was a light-hitting outfielder named Brent Lillibridge.

During the 2008 season, Lillibridge found himself shuttling back and forth between Triple-A. By September, he knew something needed to change; his swing simply did not resemble those of his more successful teammates. With so little time left in the season, Walker recommended that Lillibridge visit Wallenbrock.

Right away, Lillibridge said, Wallenbrock was able to offer the visual and verbal feedback he needed.

“I got some swings, he broke down my video, showed me the moves and things I was doing incorrectly,” Lillibridge said. “It all made sense: how he explained it, communicated it, was perfectly done.

“It’s so important to explain why something needs to happen. He’s so great at communicating something so quickly. He just knew how to teach so well, to communicate to so many big league guys in his career.”

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Dodgers beat A’s to clinch eighth consecutive NL West title Van Scoyoc was fresh out of college at the time. He’d worked with Wallenbrock in high school, and in college, and offered to volunteer at The Ballyard to begin his apprenticeship as a coach.

Once, Lillibridge recalled, “I asked Craig ‘who’s this punk?’ Craig said, I trust him, he’s my number-2. He has a great way to communicate.”

When the Dodgers, Padres and Mariners plucked their hitting coaches from the Wallenbrock tree, Lillibridge said, “I think it showed a shift in Major League Baseball of understanding the ability to communicate. Good teachers who can communicate and use technology are more valuable than a guy who played 15 years and is a Hall of Famer. It’s opening the floodgates to realizing it’s all about development – not just at the minor league level, but the major league level as well.”

When Gabe Kapler attempted to come back to the major leagues prior to the 2008 season, he reached out to Wallenbrock, who had coached him more than a decade earlier. The comeback was a success. One year after managing the Boston Red Sox’s Class-A affiliate, Kapler batted .301 for the Milwaukee Brewers.

The two reconnected again when Kapler was named the Dodgers’ farm director in 2015; that led directly to the Dodgers retaining Wallenbrock and Van Scoyoc as consultants. The shift had been set in motion. The seeds of the coaching tree were planted.

Notably, Bonds lasted only one season as the Marlins’ hitting coach. The Wallenbrock tree is only starting to spread its roots.