Every Thursday afternoon in Garden Grove, California, three dozen youngsters stream on to the Pacifica High School athletic field, their 14-year-old forms unrecognisable beneath the heavy pads and helmets of American football.
What follows is a body-bruising clash between Pacifica and an opposing team, both vying to alternately block and advance the ball.
But when the weekly game is over and the helmets and the pads come off, two of the courageous youngsters of the Pacifica High School Mariners turn out to be girls.
The school district, which initially refused to let Sarah Moranville and Sandra Berrera play full-contact football head-to-head with boys, this year reversed its own decision despite concerns about their safety. School officials learned that laws prohibiting discrimination forced them to admit girls to one of the last bastions of true male domination in American education - contact sports.
"Our primary concern was the safety of the athletes, and that doesn't matter what gender the athlete is, because football in America is not just a contact sport, it's a collision sport, and the object is obviously to make intense bodily contact," said Alan Trudell, spokesman for the Garden Grove Unified School District.
"We opted to err on the side of caution until we could research the subject, " Trudell said. The research showed that girls who were physically able and fulfilled criteria such as attendance at practices had a right under federal equal opportunity provisions to play full-contact sports.
"The reaction has ranged from supportive to mixed," Mr Trudell said. "It just depends on who you talk to. This is a new issue for our school district. But we always try to put it into perspective.We have other things to worry about. "
Participation by girls in school sports has swelled from 294,000 in 1971 to 2.3 million last year. A tiny but growing fraction are wrestling or playing football, two contact sports originally open only to boys.
Last year, 1,164 girls wrestled and 791 played football; because of physical differences, most sat on the bench in reserve or acted as kickers, who usually are unmolested by opponents.
"The opportunities have risen dramatically for participation in traditional girls' sports, but of course there are those girls who are interested in another level of competition," said Bruce Howard, spokesman for the National Interscholastic Athletic Administrators Association.
"There is obvious reluctance for safety and other reasons for girls to be involved in football and wrestling, but the law says they cannot be denied the right to compete."
Now hardly anyone in Garden Grove appears to find the presence of two girls on the football team unusual. One plays tailback, the other the position traditionally known as lineman. She prefers "lineperson".
"We've always been taught as girls that if we want something and if we've got our minds set to do it, to go and do it, not to let the gender barrier hold you back, and I'm a firm believer in that," said Sarah's mother.