A new film opens Sept. 22 — "The Battle of the Sexes" — but it's not a superhero action flick. It's about a 1973 tennis match in Houston's Astrodome, albeit one seen by 50 million American TV viewers. In an extraordinary milestone in American cultural history, 55-year-old Bobby Riggs played 29-year-old Billie Jean King. The news media billed the affair as the "Battle of the Sexes," hence the movie's title. The event proved to be a major turning point for women's tennis, the women's liberation movement and the sports entertainment industry.

The media-savvy Riggs, who was equal parts championship tennis player, carnival barker and high-stakes hustler, had issued a challenge to women tennis players in January 1971. He suggested in a follow-up Sports Illustrated interview that even at his advanced age he could beat either King or Margaret Smith Court, the two best women professionals at that time.

"It would be close on grass," he said, "but any other surface I could take them in a one-set match, two out of three or three out of five."

In his book, "Court Hustler," Riggs wrote that he confronted King at the U.S. Open later in 1971. "Why don't we play a fun match — for five thousand dollars to add to the fun — on any surface you like?" Riggs asked. Billie Jean chuckled but declined, so Riggs turned to Court.

Riggs enlisted a promoter and convinced Court to play a televised match on Mother's Day, May 13, 1973, in Ramona, Calif., near San Diego. Riggs easily beat her 6-2, 6-1 in 57 minutes.

Riggs, whose brash talk was mostly hype for the hungry media, brayed to reporters afterward about his next match.

"I want King bad. I'll play her on clay, grass, wood, marble or roller skates, he said. "We want to keep this sex thing going. I'm a woman specialist now."

Thinking that she had to defend women's tennis, Billie Jean reluctantly agreed to play Riggs, and many tennis fans remember the spectacle in the Astrodome. However, only a few know about a long-standing debate about whether Riggs threw the match to settle a gambling debt to some Florida mobsters. Was Riggs in the tank, or simply in over his head against King?

The background

The Open era in tennis that began in 1968 was a rising tide that lifted most of the game's boats, especially tournament prize money for the male pros. But the women's purses notably lagged behind.

The outspoken and spirited King championed the cause of equal prize money and TV coverage for women's tournaments. Her zeal reflected the Women's Liberation movement in the late 1960s and 1970s. Betty Friedan, Bella Abzug and Gloria Steinem were in the news, and the U.S. congress passed the Equal Rights Amendment to the Constitution and sent it to the states for ratification.

Open tennis also included senior men. Riggs was one of the graying stars who quickly gained success in the geezer tournaments. Starting in 1969, the former Wimbledon champ won armloads of trophies in U.S. national senior singles and doubles championships with deft strokes and lobs over net rushers. But the news media paid little attention to the senior men, so Riggs hit on a scheme to play King for money and a big slice of the publicity pie. But when King demurred, Riggs set up the Court match.

After Riggs, defeated Court, King knew she had to accept Riggs' challenge. She later described her thoughts at the time to writer Selena Roberts: "That's it. I've got to play him."

The match

Promoter Jerry Perenchio had watched the Riggs-Court match on TV and saw a chance to make money on a possible Riggs-King match. Perenchio had promoted the huge 1971 Muhammad Ali-Joe Frazier fight, and had helped Norman Lear and Bud Yorkin produce hit TV series including "All in the Family."

Perenchio convinced Riggs and King to agree to a match, with a purported $100,000 winner-take-all payout. In reality, each would be guaranteed $75,000, with a $100,000 kicker to the winner. Perenchio auctioned "The Battle of the Sexes" to the Astrodome for a reported $250,000, and ABC bought the TV rights for $750,000, a sum that dwarfed the rights price then for a Grand Slam tournament.

Riggs hit the talk show circuit and spewed hyperbole that the media eagerly reported. "I don't mind being called a male chauvinist pig as long as I'm the No. 1 male chauvinist pig.

"The best way to handle women is to keep them barefoot and pregnant."

Current and former tennis pros weighed in on the predicted outcome of the match between the Lobber and the Libber.

"Bobby's going to win," Pancho Segura told the media. Tennis legend Jack Kramer agreed. Women players spoke up to the media for King, and her father, Bill Moffitt, told Sports Illustrated, "Sissy Bug will murder this Riggs."

On the night of the match, the Astrodome welcomed 30,472 people, with high rollers paying $100 for a courtside seat. Four buff Rice University track and field athletes carried King to courtside on a golden throne bedecked with colored feathers. A trumpet flourish announced Riggs, who rode in a rickshaw pulled by his Bosom Buddies. The women wore tight tee shirts printed with the name of one of Riggs's sponsors, candy maker Sugar Daddy.

The two players exchanged gifts at the net just before the best-of-five match. Riggs gave King a giant Sugar Daddy caramel lollipop, and she gave him a young piglet that she had named Larimore Hustler.

King won the first game, but voiced her concern that Riggs might be loafing to her coach Dennis Van der Meer on the sideline. Van der Meer said she was seeing the real thing.

Riggs uncharacteristically double faulted to lose the first set, 4-6. According to author Tom LeCompte, a tennis insider watching on TV remarked, "Looks like Bobby bet on Billie Jean."

In the second set, King kept pressuring Riggs with her first serve. She controlled the net with sharp volleys, often wrong-footing Riggs. She also picked up Riggs' frequent lobs among the Astrodome's lights and smashed them for winners. When Riggs chipped his backhand and charged the net, King passed him. She won the second, 6-3.

In the final game of the third set with Riggs serving on King's third match point, Sports Illustrated reported that someone in the stands yelled, "Close him out, Sissy. Close him out."

Riggs followed his second serve to the net, and King hit a weak return. Riggs clumsily netted what should have been an easy put-away. Match over, 6-4, 6-3, 6-3.

Both said all of the right things to the media afterward. "She was too good," Riggs said. "She played too well. ... I couldn't get the best out of my game. It was over too quickly."

"I think this match will do great things for women's tennis," King said. "A lot of non-tennis people saw it and they know we can play now."

The fix?

In his 2003 Riggs biography, "The Last Sure Thing," LeCompte collected opinions from knowledgeable tennis people on the possibility that Riggs threw The Battle of the Sexes. Gene Mako, a member of the International Tennis Hall of Fame and an amateur contemporary of Riggs, was confident that Riggs had tanked.

"I was looking at the match on TV," he told LeCompte, "and in the middle of the second set ... I knew exactly what was going to happen." Mako was convinced that Riggs, who had a return match in his deal with King, would throw the match, and then win the rematch. "Listen, this was a man who was willing to do anything for money, anything."

Joe Fishbach, another ranked player who frequently competed against Riggs, said, "Against Billie Jean, he definitely threw it."

On the other hand, LeCompte quotes Kramer: "Bobby got beat head-up because after he clobbered Margaret Court he figured he could beat any of the dames without training."

The suggestion that Riggs purposely lost gained considerably more attention on Aug. 25, 2013, when ESPN.com published an article titled "The Match Maker" by Don Van Natta, Jr. The author quotes Hal Shaw, who describes himself as an eyewitness to a mob meeting in January 1973 at Palma Ceia Golf and Country Club in Tampa, Fla.

Shaw, an assistant golf pro, said the mobsters decided to forgive a gambling debt Riggs owed one of their bookies, and, in return, Riggs would throw the King match. Riggs had proposed a three-match parlay. He would challenge and beat Court, which would force King to play him. Riggs would then throw the King match, and the mobsters would get a big payday. Riggs would insist on a rematch provision in any contract with King, thus allowing him to play the third match straight up.

Van Natta also quotes several knowledgeable observers — Donald Dell, Stan Smith, Doug Adler, for example — on their surprise at Bobby's subpar play. Additionally, Rosie Casals noted from broadcast booth in the Astrodome that something appeared wrong.

"He doesn't look right to me," Casals said. When Bobby hit an easy return into King's wheelhouse, Casals said, "That's pretty unusual for Bobby. ... Where is Bobby Riggs? Where did he go?"

In the mid-1990s, Riggs told sportswriter Steve Flink, according to USA Today, "People said I was tanking, but Billie Jean beat me fair and square."

Van Natta reports that King and Riggs had become close friends after 1973, and King visited the failing Riggs just before his 1995 death. King reminded the dying man how much “The Battle of the Sexes” had helped women both on and off the court.

Michael K. Bohn is the author, among other books, of "Heroes & Ballyhoo: How the Golden Age of the 1920s Transformed American Sports."