A 16-year-old who won a regional tournament this week was denied the trophy because she is a girl, it has been reported.

High schooler Emily Nash shot a three-over-par 75 at the Central Massachusetts Division 3 boys' golf tournament on Tuesday, four strokes ahead of the runner up, the Worcester Telegram & Gazette reported.

The result should have seen her given the opportunity to play at the state high school golf championships.

But instead her team did not qualify as a group to compete and she will not be allowed to play as an individual under the rules of the Massachusetts Interscholastic Athletic Association.

"I was definitely disappointed, but I understand that there are rules in place," she told the newspaper. "I don't think people expected for this to happen, so they didn't really know how to react to it.

"None of us are mad at the MIAA or anything like that, but I was definitely a little bit disappointed."

The ruling has been widely criticised and has seen Nash inundated with messages of support including an Instagram post from world number three Lexi Thompson.