A federal judge ruled on Thursday that the National Football League must allow an Ohio State University sophomore to enter the league's draft this year so that he can compete to play professional football.

The NFL plans to appeal the decision, and officials of both the NFL and the National Collegiate Athletic Association condemned it for its likely effect on college players.

Jeff Pash, the NFL's executive vice president, said that young players would be hurt by not taking the time to develop their skills at the college level. "Players who complete their college eligibility have longer careers, have more lucrative careers, have more successful careers than players who don't," he said.

Wally Renfro, senior advisor to the president of the NCAA, says allowing students to jump into the NFL at an earlier age will result in more college athletes failing to complete their degrees. "If you're there three years, you have a degree in sight," Mr. Renfro says. "From an educational standpoint, we're disappointed in the court's decision."

The Ohio State player, Maurice Clarett, sought to enter the NFL draft after the university suspended him from playing college football last year for accepting improper benefits and for lying about it to investigators. He had already established himself as a star running back his freshman year, in 2002, and led the Buckeyes to a national championship that season.

But an NFL rule bars players from entering the draft until three years after they graduate from high school. Mr. Clarett, now 20, wouldn't be eligible until the 2005 draft. So he sued the NFL, claiming that the league's rule violated the Sherman Antitrust Act.

NFL lawyers defended the eligibility rule, saying that it is exempt from antitrust laws because the rule is reasonable and was devised in a collective-bargaining agreement with the players.

But Judge Shira A. Scheindlin, of U.S. District in New York, said in her 70-page ruling that the rule is not exempt, because it affects nonplayers only. In addition, she noted that the NFL first adopted a version of the rule in 1925. The union that represents NFL players was not formed until 1956 and did not become the players' exclusive bargaining agent until 1968.

"While, ordinarily, the best offense is a good defense, none of these defenses hold the line," Judge Scheindlin wrote in a ruling riddled with football puns, concluding: "Because the NFL cannot prevail on any of these defenses, the rule must be sacked."

Unless a higher court stays or reverses the ruling, Mr. Clarett will be able to enter the NFL draft, which will be held in April.

Neither Mr. Clarett nor his lawyer, Alan C. Milstein, could be reached for comment.

The NFL's Mr. Pash said he was surprised by the ruling, and he remained confident that the appeals court would overturn it. But he also said the NFL had not decided whether to seek a stay that would prevent Mr. Clarett from entering the draft until an appeals court could hear the case, which would probably happen after the draft.

If the ruling is upheld, said Mr. Renfro, the NCAA official, he doesn't expect all of college football's talent to be sapped away by the NFL. The National Basketball Association lets 18-year-old players participate, he said, yet college basketball is still popular and exciting for the fans.

But he also said that football players who skip college to go to the pros could be in for a rude awakening as they face NFL players who are much bigger and more aggressive than players at the college level.

"Football is different than the other sports because physically it's more challenging," Mr. Renfro said. "It's hard to know what the effect of that will be."

The NCAA has very strict rules that limit the compensation that college athletes can receive. Students are not allowed to receive payment or other gifts.

At the professional level, the minimum annual salary for a rookie running back in the NFL is $225,000, and the average salary for an NFL player is more than $1-million a year.

The judge has also scheduled a conference next Thursday for the two sides to argue whether Mr. Clarett should receive monetary compensation for being kept out of the 2003 draft.