KALAMAZOO, Mich. (AP) -- The Little League Softball World Series is in an uproar this year because boys who joined a girls team are playing in what has traditionally been an all-girls event.

Parents, teams and tournament officials say the five 16-year-old boys from Arizona have an unfair physical advantage, and may even pose a danger to girls. Some teams are threatening not to play the team, and the tournament director himself is protesting.

"It looks like they stacked the deck. Those boys are huge," said Val Maslauskas, a parent from a Massachusetts team whose players wore mouthguards to protect themselves in a 10-2 loss to the Arizona team Wednesday. "We're trying for equality for these girls and this is not equal."

The crowd erupted in cheers when one of the boys was thrown out at second base and booed at a collision between an Arizona boy and a Westfield girl at first base.

"They made catches in the outfield that no girl could have gotten to," said Kelly Popko, who played third base for Westfield, Mass.

Little League Baseball Inc. made its softball and hardball divisions non-gender specific in 1974 after losing lawsuits filed by boys demanding to play softball, spokesman Lance Van Auken said Wednesday.

The first girl played in the Little League Baseball World Series in 1984. The Arizona boys are the first to play in the softball series.

"Little League's preference is that the softball division be for girls," Van Auken said. "It would be nice if there were a legal solution to it."

Richie Reyes and four other boys signed up for the girls team after their usual summer baseball league disbanded. He doesn't see what the fuss is about and says the girls' team needed more players.

"We were all brought up to believe that an athlete's an athlete," he said.

Four teams have indicated they won't play the team. A Philippines team had originally threatened not to play, but players changed their minds and wound up beating the boys-and-girls squad 3-2 Tuesday night.

Describing an "undercurrent of unhappiness," tournament director Bud Vanderberg said he will take the issue to the national Little League board of directors next week.

"I will do what's in my power to change this to make sure it's all girls playing in this tournament," he said.