It was an incongruous sight for a baseball stadium: tens of thousands of ultra-Orthodox Jewish men, all dressed in black suits and white shirts, filing through the gates of Citi Field on Sunday, wearing not blue-and-orange Mets caps but tall, big-brim black hats.
There was no ballgame scheduled, only a religious rally to discuss the dangers of the Internet.
More than 40,000 ultra-Orthodox Jews were expected to attend — a sellout in a season where the average attendance at a Mets game has been barely half that. The organizers had to rent Arthur Ashe Stadium nearby, which has 20,000 seats, to accommodate all the interested ticket buyers.
The organizers had allowed only men to buy tickets, in keeping with ultra-Orthodox tradition of separating the sexes. Viewing parties had been arranged in Orthodox neighborhoods of Brooklyn and New Jersey so that women could watch, too.
For the attendees, many of whom said they came at the instructions of their rabbis, it was a chance to hear about a moral topic considered gravely important in their community: the potential problems that can stem from access to pornography and other explicit content on the uncensored, often incendiary Web.
Inside the stadium, a dais was set up by the back wall of center field, where rabbis led the packed stadium in evening prayers and offered heated exhortations to avoid the "filth" that can be found on the Internet. English translations of the speeches appeared on a jumbo digital screen, beneath an enormous "Let's Go Mets!" sign.
Still, many attendees readily conceded that the Internet played a big role in their lives.
Shlomo Cohen, 24, of Toronto, said he used the Internet for shopping, business and staying in touch with friends — "Everyone needs e-mail," he said.
Mr. Cohen said he came to Citi Field on Sunday because the rally was a good way to remind his community to keep temptation at bay.
"Desires are out there," Mr. Cohen said, adding that men could be particularly susceptible. "We have to learn how to control ourselves."
For an event billed as taking aim at the Internet, signs of the digital age seemed to pop up everywhere.
On a No. 7 train headed toward the stadium, several men wearing the clothing of the ultra-Orthodox whipped out smartphones as soon as the subway emerged from the East River tunnel, poking at e-mail in-boxes and checking voice mail messages.
Several opponents of the rally gathered outside the stadium, including a crowd that stood by police barricades holding signs that read, "The Internet Is Not the Problem."
Many of the protesters said they shared the religious beliefs of the attendees but wanted to show support for victims of child sexual abuse, some of whom in ultra-Orthodox communities have been discouraged from calling the police and have been shunned after the crimes against them were reported.
The rally in Citi Field on Sunday was sponsored by a rabbinical group, Ichud Hakehillos Letohar Hamachane, that is linked to a software company that sells Internet filtering software to Orthodox Jews. Those in attendance were handed fliers that advertised services like a "kosher GPS App" for iPhone and Android phones, which helps users locate synagogues and kosher restaurants.
Nat Levy, 25, who traveled from Lakewood, N.J., to attend, said he frequently surfed the Web at a cafe, overseen by a local rabbi, that filtered out certain types of online content and monitored which Web sites he visited.
He said he often used the Internet to deal with customers for his company. "You get to do business the same way," he said. "I have unlimited access, but it's done in a kosher manner."
Eytan Kobre, a spokesman for the event, delivered a more intense message to reporters outside the stadium. "The siren song of the Internet entices us!" he pronounced in a booming voice. "It brings out the worst of us!"
Still, Mr. Kobre confirmed that the event would be broadcast live on the Internet, via a stream available to homes and synagogues in Orthodox communities around the New York area. He said the general public would not be able to gain access, but several unauthorized streams appeared soon after the rally began.
The rally was also a hot topic on many Twitter feeds on Sunday evening.
The gathering had the feel of a gigantic family reunion — or perhaps, given the single-sex attendance, the religious version of a scouts' jamboree — but many guests had arrived with only a friend or two.
"It may look like a community because we all look the same," said Mr. Cohen, of Toronto. "But I don't know almost any of the people here."
For some attendees, the dangers of the Internet seemed more in line with the usual complaints voiced by any New Yorker tethered to a BlackBerry or besieged with Twitter messages.
Raphael Hess, 29, of New Jersey, pointed at his LG phone and said he found peace in simply keeping its Internet connection turned off.
"Life is more pleasant without it sometimes," he said with a shrug.
Laurie Goodstein contributed reporting.