Bruce C. Ratner did not pretend to be much of a basketball fan when he paid $300 million in 2004 for the New Jersey Nets. Before long, the team had the worst record in the National Basketball Association, and he had a reputation as one of the worst owners in professional sports.

But he also had the leverage he needed to pull off a real estate megadeal.

The purchase was the most glaring demonstration of Mr. Ratner’s single-minded dedication to a goal: building a 22-acre, $4.9 billion project in the heart of Brooklyn, the largest development project in the borough’s history. Though the Atlantic Yards plan also called for residential towers, a significant portion of which will be subsidized, he sold it to the public as a way to finally bring professional sports back to the borough.

“So, how did we get here?” Mr. Ratner asked last week, almost giddy, at the ribbon cutting of the nation’s most expensive basketball arena, the Barclays Center. “We first needed to buy a basketball team, and against all odds we did it.”

That acknowledgment highlights a characteristic that emerged again and again over the past nine years: Mr. Ratner, one of the most prominent and polarizing figures in real-estate-mad New York, may portray himself as a reluctant developer, but he will do what is necessary to get a deal done.