Growing up, Mike Zarren had season tickets with his father at the old Boston Garden, where they watched the legendary Celtics teams of Larry Bird, Robert Parish, and Kevin McHale. Almost three decades later, Zarren, AB’99, still catches home games in the balcony with his dad. One small thing has changed: Zarren is now the assistant general manager and team counsel.

“This isn’t a job I ever planned on getting,” says Zarren, now in his tenth year with the franchise. He’s not your typical NBA front-office executive. Zarren is one of the pioneers in the rapidly evolving field of APBRmetrics, which is a fancy way of saying advanced basketball statistics—think Moneyball with a squeaking-sneaker soundtrack. “I had been interested in mathematics. But I never used math with basketball before working for the team,” Zarren says. “The most I had done was run a fantasy basketball league” as a teenager.

Zarren never played basketball beyond high school and quiz bowl was his primary extracurricular activity at Chicago. As an economics major, he became a protégé of professor and Freakonomics coauthor Steven Levitt, who helped him develop a fascination with the value of statistics. Much to Levitt’s disappointment, though, Zarren took his talents to Harvard Law. “I was horrified. It made no sense at all to me, because law would not have rewarded his talents,” says Levitt, the William B. Ogden distinguished service professor of economics. “When he ended up with the Celtics, I was delighted.”

During Zarren’s second year of law school, the team was looking to add an unpaid statistician. Data-intensive analysis of NBA players beyond the traditional points, rebounds, and assists was still in its infancy, but the Celtics wanted to explore the potential.

Zarren joined the franchise full time in 2005. The novelty of his work and the wariness of traditionalists—Zarren’s boss, Danny Ainge, told the New York Times that Celtics coach Doc Rivers was “skeptically receptive” to Zarren’s analysis—made him a front-office curiosity. Celtics star Paul Pierce took to calling him “MIT.”

As long as the NBA establishment wasn’t quite buying this methodology, Zarren could share his point of view without fear of relinquishing a competitive advantage. His Inside the Numbers columns on the Celtics website included “Draft Lottery Demystified,” “Offensive Efficiency,” and “How to Measure Rebounding Success.”

On the surface, the last subject seems simple: you measure rebounding success by which team has more rebounds, right? Not so fast, says Zarren. Examining a 2006 game between the Celtics and the Charlotte Bobcats, he explained the flaw in that reasoning.

To Zarren, defensive-rebounding percentage—“Out of all possible defensive rebounds each team could have gotten, how many did they actually get?” Zarren wrote—matters more. Boston won that game against Charlotte, a victory largely credited to its rebounding advantage. In Zarren’s calculation, though, Charlotte was better on the boards that night—Boston’s more efficient shooting made the difference. “So though each of the major Boston newspapers claimed that a big part of the Celtics’ win was outrebounding the Bobcats,” Zarren concluded, “in fact the Celtics won this game despite being outrebounded.”

Scoring comes under similar counterintuitive scrutiny. Points per possession—as opposed to per game—determine offensive success by the APBRmetrics method. The pace of play varies from game to game, which means a team will not always have the same number of scoring opportunities. In 2006, the methodical Detroit Pistons fell in the middle of the pack in points per game but were the league’s third best in points per possession. The Pistons reached the Eastern Conference finals that season.

That same year, Boston completed a multiplayer trade with the Minnesota Timberwolves. Although its offensive production dipped slightly in points per game, Zarren showed that the Celtics moved up from 19th to 11th in points per possession after the trade—becoming a better-scoring team despite the per-game decline.

He’s less forthcoming with his analysis now. Zarren wrote seven Inside the Numbers columns over parts of two seasons, his last appearing April 23, 2007. The following year the Celtics won the NBA championship, attracting copycat attention to every aspect of the organization, including the suddenly circumspect stat guy in the stands with his dad. “We just don’t talk about what I do,” Zarren told the Boston Globe in 2008.

Knowledgeable basketball people have started to notice. Sports Illustrated referred to him this past summer as “one of the least-known yet most-influential members of the Celtics’ front office” when Zarren’s name surfaced as a candidate for the Philadelphia 76ers general manager position. He ultimately withdrew from consideration, remaining in Boston, where his career has given new meaning to the term fantasy basketball.

“I’ve been going to games with my father ever since I was a kid. And to think that now I have an NBA championship ring with our last name on it. It’s surreal.”