They’re winning on the field, but off the diamond the Oakland A’s plans for a new ballpark continue to be plagued by political intrigue and unexpected setbacks.

The latest curveball was a slick flyer produced by a group identifying itself as Protect Oakland’s Shoreline Economy that questioned the A’s move from the Coliseum to the Port of Oakland’s Howard Terminal near Jack London Square.

The mailer ticks off a list of drawbacks to the proposed move, including “severe traffic impacts” to nearby warehouses and neighborhoods and the “hundreds of millions of dollars” in taxpayer-funded infrastructure that will be needed.

The flyer even argues that an A’s waterfront ballpark would force the homeless to move their street camps to make room for fan parking and describes the team’s plan for an overhead gondola to ferry fans over the nearby railroad tracks as “silly.”

Just who’s behind Protect Oakland’s Shoreline Economy, which lists its address at an Oak Street condo complex in Jack London Square, is a bit of a mystery. But the group’s mailer appears to be an attempt to stir up the type of neighborhood opposition that killed the team’s first choice for its new ballpark: next to Laney College near downtown Oakland.

Adam Simons, a spokesman for Schnitzer Steel, which has raised concerns about having the ballpark next door to its scrap recycling plant, tells us his company had “zero involvement” in putting out the piece.

Nor apparently did political consultant and former state Sen. Don Perata, who has been advising the company. However, he told us the language from the flyer appeared to be cribbed directly from a report he prepared a couple of years ago for the Oakland-Alameda County Coliseum Authority board of directors when they were trying to make a case for the A’s to remain at the Coliseum.

Perata did point us to business management consultant Robert Apodaca, who he said helped found the largely “under-the-radar” group Protect Oakland’s Shoreline Economy three years ago to put a check on other development plans in the Jack London Square area. Apodaca, who lists his business at the same Oak Street address as POSE, didn’t return our call seeking comment.

A’s President Dave Kaval said he didn’t know who is behind the mailer, nor had he heard any of the complaints it lists from neighbors of the site.

To the contrary, Kaval said, many Jack London Square area residents and businesses see the ballpark as a “catalyst” for improving the neighborhood, including getting more guardrails and other safety features along the railroad tracks. That would eliminate the constant irritation of train engineers sounding their horns when passing through the area.

Kaval also rebutted the idea that Howard Terminal would come with significantly higher public infrastructure costs. He said rebuilding at the Oakland-Alameda Coliseum — where they currently play — would require an infusion of “hundreds of millions of dollars” as well.

Meanwhile, there are questions about the team’s alternative plan for a new stadium at the Coliseum.

In May, at the urging of Mayor Libby Schaaf, the Oakland City Council voted to give the A’s an exclusive nine-month option on the Coliseum site while team management also talks with the port. But, it turns out, city leaders never signed the paperwork to make the agreement official.

Council President Larry Reid told us the Coliseum deal was hung up on a few technicalities — one of them efforts by the city to buy out Alameda County’s half-interest in the $160 million Coliseum site so it could have full control over any development there.

Schaaf’s office declined to comment, referring us instead to Karen Boyd, spokeswoman for the city administrator’s office. She partially blamed the holdup on “scheduling challenges” but said, “We are working cooperatively with the county to answer questions, and we are proceeding ahead with all parties in good faith, honoring the terms” of the exclusive negotiating agreement.

In the meantime, Kaval, frustrated by the city’s apparent inaction, has quietly reached out to the Alameda County Board of Supervisors to discuss the possibility of the team buying out the county’s half interest in the 120-acre site.

Supervisor Nate Miley confirmed that the county was in talks with the A’s about the team acquiring the county’s stake.

“We are not concerned with whether Oakland is happy or not — we are looking at our interests, and our bottom line is to get out of the sports business,” Miley said. “And if the city can’t help us do it, then (the hope is) to get out of it with help from the A’s.”

Kaval insisted the A’s weren’t going behind Oakland’s back, noting the team had a standing offer on the table to buy the entire Coliseum site from the city and county for $137 million.

However it plays out, Kaval said, the team is continuing to try to nail down a new ballpark location by the end of the year.

“We are just trying to hit our deadlines and get a stadium built on our time line,” he said. “We don’t want to get pulled down in politics.”

San Francisco Chronicle columnists Phillip Matier and Andrew Ross appear Sundays, Mondays and Wednesdays. Matier can be seen on the KPIX-TV morning and evening news. He can also be heard on KCBS radio Monday through Friday at 7:50 a.m. and 5:50 p.m. Got a tip? Call 415- 777-8815, or email matierandross@ sfchronicle.com. Twitter: @matierandross