Oakland, Calif.— As a much-anticipated federal trial began here Monday, the walls that have long separated college athletes from the riches of a multibillion-dollar sports enterprise began to show some cracks.

The occasion was the opening of an antitrust lawsuit filed on behalf of current and former men’s basketball and football players. It seeks an injunction against the NCAA that would effectively allow athletes to profit from the use of their names, images and likenesses in television broadcasts, rebroadcasts, video games and more.

Lead plaintiff Ed O’Bannon — a star UCLA basketball player in the 1990s — took the stand first, stating that he spent 40 to 45 hours a week on basketball during the season, choosing a major that would fit with his schedule and taking his senior finals in a hotel ballroom during the Final Four.

“I was an athlete masquerading as a student,” said O’Bannon, now a 41-year-old automobile sales and marketing employee in Las Vegas. “I was there strictly to play basketball … and I did basically the minimum to make sure that I kept my eligibility academically so I could continue to play.”

The issues raised — whether student-athletes should receive a greater piece of the collegiate athletics pie than the scholarships they are granted — goes far beyond this trial.

Before O’Bannon began his testimony, a lawyer for the NCAA announced that it had reached a settlement to pay $20 million in damages in a related case brought by former college quarterback Sam Keller. Keller sought compensation for Division I football and basketball players whose likenesses have appeared in NCAA-licensed video games.

It follows a May 31 settlement by Electronic Arts and Collegiate Licensing Co., which agreed to a $40-million payout to thousands of football and basketball players.

Northwestern University football players are pressing to form a union to seek larger scholarships and better medical care as university employees. Another case headed for the courtroom here aims to end the NCAA’s cap on athletic scholarships, contending that they do not cover the full cost of attending school.

The payments in the video game litigation will go to every player whose likeness appeared in EA Sports video game products — now phased out — over the last decade or so. The Keller case alleged the companies had colluded with the NCAA to deny players their rights under state laws to their names, images and likenesses.

The antitrust issues raised in the O’Bannon case — that the NCAA has engaged in a price-fixing conspiracy and group boycott, distorting the market — are not directly affected by the settlements and NCAA officials denied that its decision to pay represents a change in the rules that forbid athletes from receiving so-called “extra benefits.”

“In no event do we consider this settlement pay for athletic performance,” Chief Legal Officer Donald Remy said in a statement.

But the underlying premise of the 108-year-old NCAA — that players are students first, compensated through their scholarships and overall collegiate experience — is nevertheless at stake.

“The really big issue is whether the court finds these NCAA [amateurism] rules to be illegal,” said Matt Mitten, director of the National Sports Law Institute at Marquette University. “That could bring a very substantial change.”

O’Bannon testified that a friend’s son showed him an Electronic Arts video game in 2008 that included his likeness — a UCLA player with his jersey number, 31, who shot with his left hand, was bald and had the same complexion as O’Bannon. The lawsuit followed.

A star Artesia (Calif.) High School player, O’Bannon estimated that he had been recruited by 50 schools. When he committed to UCLA as a 17-year-old, he testified, he signed documents without reading them — including a waiver that allegedly gave the NCAA the right to use his likeness — because if he hadn’t he wouldn’t have been able to play.

In his cross-examination of O’Bannon, Glenn Pomerantz, the NCAA’s chief outside counsel, stressed the amateur nature of student athletics by focusing on the overall college experience of mentorship and community and the direct benefits of a scholarship: tuition, free books, room and board — including access to a buffet “training table.”

O’Bannon chose to stay with the Bruins in 1995 — though he could have gone to the NBA by then — and helped the team win the NCAA championship. He was named the game’s most valuable player.

“Is it fair to say that season changed your life?” Pomerantz asked.

“Yeah, I think it is,” O’Bannon answered.

Asked if he knew whether proceeds from broadcast contracts were used to pay for student-athlete scholarships, O’Bannon said he did not.

Remy, in a statement, reiterated the NCAA’s belief that “the current system of college athletics — bolstered by continual improvements — provides the greatest opportunities to the most student-athletes by not paying those who play only Division I men’s basketball and football.”

“The collegiate model of sports provides hundreds of thousands of student-athletes with unmatched opportunities for education, growth, mentoring and future success,” he said.

O’Bannon acknowledged on the stand that he had said in a 2011 deposition that current student-athletes are amateurs but said he now feels differently.

“I’m not talking, you know … X certain amount. That’s for someone else to figure out. But with the amount of money that they are bringing in, I think that they should be compensated,” O’Bannon said.

Stanford University economist Roger Noll also testified Monday. He said fixed scholarship amounts and the denial of student-athletes’ ability to shop their own names, images and likenesses amount to a “price-fixing” agreement among the NCAA and its member institutions and conferences that is enforced through rewards and punishments.

“That’s exactly what a cartel tries to do is prevent the members from pursuing self-interest to its natural outcome,” he testified.

Robert McCormick, an emeritus law professor at Michigan State University College of Law who has long studied the NCAA, said regardless of the outcome in the O’Bannon trial, the flurry of cases represents “a substantial questioning of the NCAA system in which they use this valuable labor and don’t pay for it, and reap tremendous financial bounty.”

“Attitudes change slowly, especially in something as dear as college sports,” he said in an interview, “but I think attitudes are beginning to change about the treatment of these young men by their universities and by their trade organizations.”

The trial is expected to last up to three weeks, but U.S. District Judge Claudia Wilken will not rule from the bench.

Her ruling will probably be appealed. Upcoming testimony is expected from more athletes, including former University of Alabama wide receiver Tyrone Prothro, as well as from NCAA, university and conference officials.