It is “good news for San Francisco,” Mr. Rosentraub said. The city gets an arena without paying for it — an enviable position — and “tip your hat” to the entrepreneurs for knowing they have to pick up the bill, he said.

Sam Singer, a spokesman for the opponents, countered that there were tens of millions of dollars in “hidden” costs involving transportation, parking and police staffing.

The public relations battle rages on. And each side is well armed. The Warriors have retained a former spokesman for Willie Brown, the onetime mayor of San Francisco. The opponents have landed one of the city’s best-known operatives, a political consultant named Jack Davis, who successfully ran three San Francisco mayoral campaigns and was described by The San Francisco Chronicle as “one of the most feared and loathed political players” in the city.

Mr. Davis, 68, got involved in the fight not because he is antigrowth or outraged by gentrification, but as a personal favor to Mr. Spaulding. When Mr. Davis’s brother, who lived in Arizona, learned he had cancer, Mr. Davis told him to get on a plane to San Francisco and go to U.C.S.F. He told him, “I’ll call Bruce Spaulding and get you squared away with the best doctor you can find.”

Shortly after that, Mr. Davis, who now lives part time in Wales, came to San Francisco and told Mr. Spaulding: “I owe you big time. Is there anything I can do for you?” He said his longtime friend answered, “Yeah, there is,” and told him about the arena. And Mr. Davis said, “Oh, yeah, sure, count me in.”

Mr. Davis, who relayed this story via FaceTime from Wales, said his goal was to help the alliance — he called it “a group of billionaires” — get on the map. “So I decided the right way to do it was to go right into the lion’s den and start a brawl.”

He succeeded. On April 30, at a fairly standard informational meeting at the nearby Mission Creek Senior Community, Mr. Davis stood and gave what several meeting attendees described as an acerbic presentation that was out of character with what had been months of tame negotiations. He was “so combative that he drew boos and hisses,” read a piece in the next day’s San Francisco Chronicle. Mr. Davis said arena opponents would not stop until the Warriors project was undone, adding, “There will be litigation until the cows come home.”