On their own or in small groups, with notable publicity or little fanfare, retired pro football players have been filing lawsuits against the National Football League, claiming the sport withheld information related to head trauma suffered while playing the game.

There are more than 85 suits involving more than 2,000 former players. On Thursday, their attorneys are expected to file a master complaint in U.S. District Court in Philadelphia that essentially coalesces all of the claims — from negligence and fraud to wrongful death and civil conspiracy — into a single document.

The outcome of this step remains uncertain — the NFL in August will likely file a motion to dismiss — but it will heighten awareness of the unprecedented string of lawsuits and provide an additional distraction to a sport already contending with questions about whether the game has grown too violent.

“The sheer number of players is certainly noteworthy,” said Michael McCann, director of the Sports Law Institute and a professor at the Vermont Law School. “It’s more than the number of players in any one season.”

While the issue of excessive violence in football — dramatized this offseason by revelations of a bounty system operated by the New Orleans Saints in which players were rewarded for injuring opponents — has been in the spotlight, public opinion is beginning to form around the need for action, according to a new Washington Post poll.

More than half the public thinks the problem of concussions in the NFL needs to be dealt with, according to the survey. Still, nearly nine in 10 fans say reports about head injuries will not make much difference in their plans to watch games this fall.

Even while the physicality of the game has long been celebrated, the Post poll found that fans prefer seeing scoring plays to big hits by more than a 3-to-1 margin.

While attention paid to the issue of player safety has already brought about rule changes in the NFL in recent years, analysts say they’ll be watching for a trickle-down effect from the lawsuits brought by retired players. As the sport’s history comes into better focus, these analysts say, the future of the NFL, a league that brings in more than $9 billion in revenue annually, becomes less certain.

“One of the worst things that can happen to the NFL is if they beat these cases in court,” said Von DuBose, one of the plaintiff attorneys. “From a legal standpoint and monetary standpoint, that’s good for them. But the public perception is going to be the that the NFL escaped on a technicality and they’re unwilling to do anything to help these guys long-term.

“It’s going to further influence people. The sentiment is going bleed down to the high school and youth football ranks. Parents are going to look at the sport and say, ‘Why would I let my son play?’ ”

Chasing change, or dollars?

The first lawsuit was filed less than a year ago, and new ones have been added almost weekly since then. Pro Football Hall of Famers (Washington’s Art Monk, Indianapolis’s Eric Dickerson, Philadelphia’s Tommy McDonald, Dallas’s Tony Dorsett), Super Bowl winners (Washington’s Mark Rypien, Chicago’s Jim McMahon) and Pro Bowlers (Baltimore’s Jamal Lewis) have all attached their names to claims.

So many have piled on that dozens of ex-players are inexplicably named in more than one suit. And some lawyers were in such a hurry to file, they cut-and-pasted other casework and forgot to change biographical data to match their clients.

Players insist this isn’t a money grab. Their goal isn’t simply restitution; they want change. The class-action lawsuits request medical monitoring, an expensive undertaking that would provide access to medical testing and services to treat any symptoms or conditions related to head trauma.

For now, the NFL is not taking issue with the science or debating the merits of the players’ claims. For the league, the matter is a procedural one.

“I think we feel confident that these claims are subject to resolution under the collective bargaining agreement,” said Beth Wilkinson, the prominent Washington attorney who serves as the NFL’s outside counsel on the matter.

The NFL will argue the CBA, which governs the relationship between the league and its players’ union, is the only mechanism for dispute resolution and a civil court is not the proper venue to handle such grievances.

This argument will likely require several months to resolve. If the NFL successfully makes its case, most players will have little recourse and the numerous claims will be moot.

“I feel strongly this judge wouldn’t do that,” said Thomas Girardi, a prominent California attorney who has obtained more than 30 verdicts of at least $1 million, including a case popularized in the film “Erin Brokovich.” “It would be so unjust to so many innocent people.”

The players will argue the CBA doesn’t govern claims by former players — particularly those who played when no CBA was in place — and the NFL was negligent in informing players about the risks of head trauma. They’re hopeful the case will reach the discovery phase, so the league might have to show what it knew and when.

Going public with problems

While penalties, rule changes and equipment upgrades might indeed help today’s football stars, attorneys say many of yesterday’s players endure a daily struggle because of head trauma they suffered while active in the game.

“For the longest time, guys dealt with this in private. They didn’t know others were experiencing the same sorts of problems,” said Girardi. “It’s embarrassing for these guys to talk about. If you break your leg at the office, you hobble around, but it’s not embarrassing. But when you talk about having a little mental problem, that’s pretty difficult for these guys to talk about.”

If U.S. District Judge Anita Brody rules the cases can proceed through the court system, the players will still face several challenges. Legal analysts say they’ll have to prove the NFL was aware of potential dangers and purposely withheld or concealed this information; and players must show specifically that the NFL was responsible for health issues that cropped up many years later.

“If we’re talking about, ‘Are people suffering as a result of playing football over many levels?’ — the question is how much of that harm is the NFL responsible for?” said Paul Haagen, a professor at the Duke University School of Law. “I suspect everybody who is good enough to play at the NFL level also had some kind of head trauma in Pop Warner, high school, college.”

Haagen says any health issues later in life could be complicated by other risk factors, such as drugs, alcohol and other unhealthy activities, though players point to myriad studies that link head trauma to depression, dementia and chronic traumatic encephalopathy.

The sheer fact so many players banded together already represents a significant step, legal experts say.

“So often in sports, players don’t sue,” said McCann. “I suspect because they don’t want to look wimpy, they don’t want to file a lawsuit. But now the culture has changed. The NFL has become a litigious culture, which marks a dramatic change.

“That’s probably a warning to other leagues. Players are turning to the court system to seek redress. The dynamics of players being afraid to sue are long over.”

Polling manager Peyton M. Craighill and assistant polling analyst Michael Brandon contributed to this report.