Where else, he wondered, have the fans preceded the team?
"It's a real Philadelphia story," said Bell, recently relocated from Los Angeles, where he directed music performances and short documentaries. "Their sole purpose was to get a team for the city that they loved. It's just amazing to me."
The Union open their 2013 season on Saturday at PPL Park on the Chester City waterfront. Fans might not recognize all of the players, because of a changing Union lineup, but they know the Sons of Ben - who pack the 2,000-seat River End stands, keeping up a drum-banging, flag-waving enthusiasm and leading the crowd in chants and songs.
The movie, simply titled Sons of Ben, is expected to premiere in early 2014.
"It's kind of crazy," said Bryan James, the cofounder and first president of the SOB. "You do something for a specific purpose, not envisioning its impact beyond its initial goal, which was to get a soccer team here in Philadelphia."
What's more, the SOB's success has provided a playbook for hopeful fans in other cities.
In Indianapolis, fans who united as the Brickyard Battalion landed a pro team in the second-division North American Soccer League. In New York, the Borough Boys helped revive the Cosmos in the NASL.
The story of the Sons of Ben, and the Union, is one of odds overcome. And if it's a little early for nostalgia - the Union are set to begin just their fourth season - it's still a great tale.
Many predicted soccer would fail here, as it had with the Atoms and the Fury in the 1970s. The Union proved otherwise, making the playoffs in their second season, and hosting exhibitions against top foreign clubs like Celtic FC and Manchester United. Last year, despite a miserable 10-18-6 record, the team drew an average 18,053 fans per game to 18,500-seat PPL Park - 98 percent of capacity.
Many doubted that fans would venture to Chester, with its reputation for crime and violence. In a trailer for the film, Sons of Ben members recall their initial reactions: "You're going to put my passion, soccer, in the place where I really don't want to go?" says Corey Furlan, now the group's vice president.
But the region wasn't going to get a team if the stadium wasn't built in a place like Chester. Putting it in Philadelphia was too expensive. Building in Chester meant funding could become available for what government officials characterized as a jobs-and-development package.
One theme of the film is how the Sons of Ben came to embrace Chester, creating the Help Kick Hunger campaign, which collects money and canned goods for the Bernardine Center, a social-services agency.
"They didn't have to do that," former Chester Mayor Wendell Butler says on film. "They could have just been the Sons of Ben."
The SOB monetary donation alone has grown from $1,500 to $20,000.
"We're not just coming into Chester to go to a soccer game and leave," SOB philanthropy director Brad Youtz said in an interview.
The chance to see a game was a long time coming.
When MLS began play in 1996 with 10 teams, people expected Philadelphia would soon join the league. Instead, a decade passed while stadium plans and ownership groups came and went, and cities like Salt Lake City and Houston got teams.
In 2006, MLS was again thinking expansion, and a small number of fans here began talking. The Sons of Ben was founded the next year - on Jan. 17, Ben Franklin's birthday.
Membership jumped from a few dozen to several hundred as the SOB became an organized and effective force, lobbying MLS officials and state politicians, and gathering thousands of signatures on petitions.
"All of a sudden these guys in blue started appearing in the strangest places," league Commissioner Don Garber muses on film.
By January 2008, expansion had become a two-city race between Philadelphia and St. Louis. The next month, Bell happened to be watching TV when he saw the official announcement that Philadelphia had won. He noticed Commissioner Garber posing with a soccer ball beside ... could that be Bryan James?
Bell knew James not as head of the Sons of Ben, but as a childhood friend from Wilmington. They grew up on the same street, Rothbury Road, spending winters tossing snowballs and summers hitting Wiffle Balls. At Brandywine High School, they tooled around in Bell's beat-up Volkswagen.
At their 20-year high school reunion in late 2011, Bell talked to James about making a movie. James didn't think his friend was serious.
He was: In March, Bell and a crew from Rothbury Road Productions flew here for the Union home opener. They returned in July to shoot during all-star week, and they plan a third visit this season.
"We knew the story was kind of cool, but we never thought anybody would make a movie about it," said Matt Ansbro, president of what is now a 2,700-member SOB.
Bell estimates the shooting is 85 percent complete. The goal is for a small theatrical release followed by entrance into film festivals and foreign markets.
"Until this is on the screen, it's all we think about," Bell said. "It's more than a soccer movie."
For more information, see www.sonsofbenmovie.com.
Contact Jeff Gammage at 215-854-2415, firstname.lastname@example.org, or on Twitter @Jeff Gammage.