Noor Alexandria Abukaram has played three high school sports since she began wearing a hijab in 2016. But she said that it was not until last weekend — after her seventh cross-country race of the season — that she learned she wasn’t allowed to run in her head scarf without special permission.

The decision by the Ohio High School Athletic Association official to disqualify Ms. Abukaram, 16, last Saturday was met with outrage on Thursday, one day after she wrote about the episode on Facebook. In an interview, she said, “It was like a nightmare came true.”

“We just found out we were going to make regionals and we were ecstatic, my whole team, so we went over to check our placing in the race,” Ms. Abukaram said in an interview on Thursday. “I went out to where they put the papers up, but my name wasn’t there.”

Ms. Abukaram said that part of her had always worried that an official might give her trouble for her hijab during uniform inspection before a race, when athletes are sometimes told to change into clothes that correspond more closely to regulations.