What qualities made Billy Beane a successful manager in Moneyball?

Michael Lewis’ Moneyball tells the story of the early days of implementing statistical analysis to select baseball players and assemble teams. It follows Billy Beane’s transformation of the under-performing Oakland Athletics through the use of these measures and initiatives. The qualities that made Billy Beane a successful manager include his ability to seek out non-traditional methods—in other words, to think outside of the box—and his willingness to take risks. In addition, his extensive knowledge of the game, his history as a baseball player himself and his willingness to break with the conventional system in order to implement controversial initiatives all helped him become a successful manager who turned the Oakland A’s around.
In Moneyball, Billy Beane essentially discards the traditional means of choosing players in favor of the statistical approach that was based, in part, on theories advocated by baseball writer Bill James. At the time, Billy Beane’s scouts scoffed at this new approach until it became clear that Billy was achieving results that far exceeded expectations. Specifically, the team won more games than most other teams in the league, despite significant budgetary constraints.
Billy Beane also had a first-hand understanding of the limitations of the traditional system. He had been scouted as a high school student himself and he never fulfilled his promise as a player. In fact, the book relates his story in the first chapter.
Although Billy met the scouts' criteria, he never translated the potential they saw in him into on-field performance. That experience was likely a major factor in his willingness to try a new system.

Billy Beane's pragmatism as well as his willingness and ability to think creatively about problems both enable him to become a successful manager, as depicted in both the book and the film titled Moneyball.
Beane's pragmatism enabled him to stay focused on his goals, undistracted by the pressures and the frustrations of his role as manager of the Oakland Athletics. He understood the limits of his situation and worked within the constraints, instead of seeking a solution beyond them. A less practical individual in his situation might not have relied so heavily on hard data, choosing instead to rely on soft methods of reasoning like intuition or guesswork.
As manager of the Oakland Athletics, Beane was able to work within the terms of challenging financial limitations, and here is where his creative mindset served him well. Instead of spending money on expensive players, Beane sought out promising talents that other managers and teams deemed imperfect, bringing together a much better team of players than his budget seemingly would allow.

Billy Beane was willing to challenge the system that made baseball successful in the first place. This innovation and confidence, as well as the determination to stick to his guns, made him an excellent manager. What he did to revolutionize the sport of baseball was incredible in that it went against every standard and convention that the sport had in place. He opted to sign less traditionally skilled players and only use the statistics he felt were vital to the success of a team and ended up creating an inspiring team that was shockingly effective.
Without Beane's perseverance, innovation, and grit, he would never have succeeded in changing the sport and making it a statistics-based sport. Doing this revolutionized the industry and changed the landscape of sports forever. Those qualities made him both an effective manager and an important innovator.

Michael Lewis attributes Billy Beane’s success as a manager to a combination of insight into the game, a broad understanding of how multiple components interacted to form a team, and deft handling of the players’ egos and emotions as well as their talents. Lewis reveals that Beane—much like his players—was not an outstanding star in one particular area. Rather, along with more than minimal competence in many areas, he would swiftly evaluate when and how to refocus his attention: he was both flexible and efficient.
While these qualities might describe all good managers, Bean brought a specific skill set related to data collection and analysis, known as “sabermetrics.” He examined at the micro level specific skills of each potential player, and built a team in which the players’ strengths truly complemented each other, rather than aiming to acquire over-priced, less versatile talent.

Billy Beane's innovation as well as his willingness to break the status quo and put his reputation on the line for his ideas made him a very successful general manager for the Oakland Athletics in the movie Moneyball and in real life.
The core nugget of Beane's success comes from his use of sabermetrics, which was then a brand new and unheard of way of evaluating how good a baseball player is. Instead of relying on scouts to make educated guesses on how well someone played ball, Beane's sabermetrics took precise measurements of all of a player's skills and abilities, and used them to compare players, finding hidden weaknesses in some and strengths in others. Beane then used the weaknesses of the players on his opponents' teams to win games, and the hidden strengths of other players by signing them to seemingly low-paying contracts that they would then outperform.
In Moneyball, Beane's use of sabermetrics is very simplified, and largely consists of his interest in a batter's on-base percentage, rather than their batting average. This creates tension between Beane and his scouts, who have used batting average as the defining characteristic of a good hitter for their entire careers, and leads to Beane signing David Justice and Scott Hatteberg. While these two players have batting averages that are sub par, their on-base percentage is well above the league average, making them valuable players. The result was a baseball team that tied for the best record in 2002 (at a phenomenal 103-59) despite having one of the lowest team payrolls in baseball.
https://www.baseball-reference.com/leagues/MLB/2002-standings.shtml