There is not much money in the sport, for anyone. Only a few of the top players and coaches on the top teams are paid. Everyone else has to pay dues to play, to create a fund for equipment, field rental and travel to away games.

Still, the sport draws Poles from every walk of life. “We have everyone,” said Roman Iwanski, president of the Eagles, as he swatted away huge swarms of mosquitoes at a late night practice in northern Warsaw. “People from all walks of life, from unemployed to doctors and lawyers.”

Mr. Sledzinski chronicled the sport’s recent explosive popularity.

“In 2006, when we formed the league, there were four teams,” he said. “The second year, there were nine teams. Then 17, 22, 35 and now more than 70.”

The first of two crucial turning points came in 2009, when a team first hired an American player to come to Poland. Now, all the top teams have at least one American player, usually a college athlete who didn’t make it into the N.F.L., and it has raised the level of play considerably. Then, in 2012, the championship game was one of the first events held in Warsaw’s new National Stadium, drawing a curious crowd of 23,000 and giving the sport a burst of publicity.

The roster of teams now includes eight so-called top teams, like the Eagles, and 10 Division 1 teams, 22 Division 2 teams and dozens more junior league and indoor arena football teams. There is even one all-women’s team, the Warsaw Sirens.

“Our colors are pink and black,” said Kamila Glowacz, 29, the team’s president. “You know, because we’re girls.”

The team got started when some of the women visited America and happened to see a game. “Many men told us we should go to the kitchen, not to the field,” she said. “But women, you know, we do what we want to do.”