But proponents of the rule point to data that shows that girls’ lacrosse has the fifth-highest rate of concussions in high school sports — only football, ice hockey, boys’ lacrosse and girls’ soccer rank higher. As the Florida High School Athletic Association board of directors was deliberating on whether to approve headgear, it heard emotional testimony from a mother whose daughter had sustained a devastating head injury while playing lacrosse.

“Our board felt it had to do something to provide a level of safety that wasn’t there,” said Dr. Roger Dearing, the Florida high school association’s executive director, whose organization oversees about 4,200 girls’ lacrosse players on 152 teams. “If the goalie in girls’ lacrosse wears a helmet because it’s hazardous to get hit by a ball, then why should the other players be unprotected? If the rule prevents one athlete from a head injury, it is worth it.”

But adding to the backlash against the rule was the Florida board of directors’ decision to ignore the advice of its own operations committee, which unanimously recommended against the new rule. Coaches and parents of athletes appeared before the board to speak out passionately against the measure. US Lacrosse representatives also attended the meeting to contest the rule, explaining how similar measures had been considered in Maryland and New York — and experimented with in Massachusetts — before eventually being dropped.

US Lacrosse, which writes the sport’s rule book authorized by the National Federation of High School Associations, asked Florida officials to delay their vote because US Lacrosse was hoping to propose its own specifications for standardized and lab-tested headgear for girls. It would then recommend voluntary use.

Nine of 14 Florida board members voted for the new rule, eager for it to go into effect this year. The decision did not quiet the opposition.