Defending Virginia AAA volleyball champion Forest Park will have to forfeit its Northwestern Region quarterfinal victory from Tuesday night for using an academically ineligible player, the school announced yesterday after discovering the mistake.

The forfeit will end the season for the Bruins, who were trying to qualify for the state tournament for the fourth consecutive year.

Don Brown, activities director at the Woodbridge school, said that all the Bruins' marks were "great" at the interim grading period about a month ago but that the marks were not checked at the end of the nine-week period.

The grades of one player, who was not identified, had dropped below Prince William County standards between the interim period, when she had four A's and two C's, and the time when report cards were issued Tuesday, Brown said.

The girl had played in the Bruins' 25-16, 25-19, 20-25, 26-24 home win over Stonewall Jackson in the region quarterfinals on Tuesday. Stonewall (17-5), instead of Forest Park, will play at 6:30 tonight in a region semifinal at E.C. Glass High School in Lynchburg. The Bruins' season ends at 16-6.

Forest Park Coach Dan Jones, the 2003 All-Met coach of the year, said one of his assistants learned of the player's grade slippage yesterday morning when stopped in a school hallway by a guidance counselor. School personnel then reported the infraction to county, region and state high school athletics authorities.

"It was an oversight on my part," Jones said. "There are checks and balances and I'm supposed to check that and didn't do it. Things across the board looked pretty healthy at midterm. . . . If anyone deserves the blame, it certainly should be me."

Jones met with his players after school yesterday and informed them that the season was over.

"The bottom dropped out of the floor and jaws dropped and tears . . . just a whole mix of emotions," Jones said. "Students were in shock, in disbelief."

Stonewall Coach Jessica Hruska learned of her team's second chance when an assistant principal delivered the news to her during an oceanography class early yesterday afternoon. After class, she scrambled through the halls to alert her players.

"They're very pumped," said Hruska, whose team, almost entirely seniors, has won eight straight matches, including the forfeit. "We can't take this for granted at all and [need to] use what's been handed to us."