The NFL has insisted since March that it would play its full 2020 season, despite a coronavirus pandemic that froze sports around the world. For that to happen, the league must navigate an intricate labyrinth of policy changes, medical interventions, business concessions and philosophical shifts, some of which were inconceivable a few months ago and have created new doubts recently as cases have risen in parts of the country.

Details of a plan have trickled out, most recently in a 13-page joint memo with the NFL Players Association that laid out the conditions necessary to allow players back into team facilities. As with other sports, it divides team employees into tiers to adjudicate access to the building and one another.

NFL owners will meet Thursday via conference call to discuss the status of plans for training camp and beyond. The specifics could evolve over time, but the big picture will remain constant. With the help of an ethicist and an epidemiologist, we identified five guiding principles the NFL should follow as it prepares for the 2020 season.

Establish the acceptable risk

Public discussion of playing amid a pandemic has focused more on process than on ethics, ignoring a mortality rate that has been estimated at 1.4%. By its nature, football might be the most difficult sport to implement mitigating policies, at least during games. Put bluntly, those who participate in on-field activities -- where masking won't often occur and physical distancing isn't possible -- will assume a new level of risk to their lives.

Don Heider, executive director of the Markkula Center for Applied Ethics at Santa Clara University, said that NFL owners should have an uncomfortable but necessary conversation about that risk. The return of football would undoubtedly boost the common good, but at what cost?

"They should think in advance about what the acceptable thresholds will be," Heider said. "Is the value that resuming football brings worth the risk? How many lives would you be willing to give up to have football games on Sunday? It's a tough question they should know the answer to before this starts. The people making those decisions have a serious financial stake in it. We all know that. But it becomes a very difficult question, because the safety thing seems almost insurmountable [to negate all risk]."

Indeed, the NFL has already conceded that some infections will occur. The challenge, according to NFL chief medical officer Allen Sills, "is to identify them as quickly as possible and prevent spread to any other participants." That approach would not only minimize spread to teammates but also to family members and others at home.

The basic conceit of football naturally leads players to take heavy risks on their short- and long-term health. This risk here is different -- and it extends to coaches, officials, medical providers and other essential personnel -- but we are already beginning to see the parameters of the discussion. The most visible example has been a handful of Tampa Bay Buccaneers players, including quarterback Tom Brady, who participated in a group workout this week despite a recent warning from the NFLPA to avoid them.

Baltimore Ravens coach John Harbaugh, meanwhile, told reporters this week that he's "not one personally to run scared from a virus or anything else." Harbaugh said that he will "respect the protocols" but added, "I'm not going to run for cover and I don't think the NFL is either."

Washington Redskins defensive coordinator Jack Del Rio, who also played in the league for 11 years, tweeted: "I think most players understand the risk of playing the game of football. The priority is not trying to be perfectly safe. ... If so, perhaps you should never drive your car."

But the NFL also has two other ethical responsibilities, according to Zachary Binney, an epidemiologist at Oxford College of Emory University. First, the league's testing regimen shouldn't leave other parts of the country short of supplies. But in a larger sense, Binney said, the NFL's return can't threaten public health by being a source of spread. It's a key underlying factor in deciding how many fans to allow in games, if any at all, and deciding the extent to which on-field participants will be separated from society. At the moment, the NFL has not finalized any plans for the potential admission of fans into games.

"No sport should be the source of a major outbreak or a contributor to it," Binney said. "That's another reason it's so important to have strict protocols. Because if players get sick, and then they go home and get their families sick, and their kids go out and get other kids in school sick, and that spreads it to other families, then that becomes a huge negative on public health. That's something they would be responsible for."

Determine where football and social distancing intersect

Football is played by large groups of men in close quarters, with frequent shouting and heavy aerobic breathing -- all commonly accepted ways of spreading the coronavirus. The point of social distancing is to keep people away from the range of individual spread. Servicing those disparate natures is a central question of football during a pandemic.

Los Angeles Rams coach Sean McVay is among many who wonder whether it's even possible.

"I mean, we're going to social distance, but we play football," McVay said during a conference call earlier this month. "This is really hard for me to understand all this. ... I don't get it. I really don't."

In a June 7 memo, the NFL and NFLPA asked teams to rearrange locker rooms, remove furniture and otherwise develop protocols to ensure that players and coaches remained 6 feet away from one another whenever possible. They provided instructions on creating one-way traffic through team facilities, mandated individual appointments with trainers, limited weight room workouts to 15 or fewer players, asked for virtual meetings wherever possible and limited in-person meetings to 20 people. Those practices likely will force teams to build temporary locker rooms, revamp their entire weekly schedule and change basic conventions of NFL life.

Then, of course, the distancing conceit would vanish for three hours on the field, as McVay noted. The NFL and NFLPA are working with manufacturers to develop a face shield that could help limit spread during a game, but such efforts are considered a supplementary tool. The most valuable intervention, Binney said, is following strict distancing protocols between games.

"The important thing for the NFL," Binney said, "is that you have to make a big upfront investment to make sure that there is a low chance that anyone who gets on the field is infected. That's the whole point of what you're trying to do during the week. It has to be done."

Understand the impact of a 'second wave' and/or flu season

Much of the long-term messaging from public health officials has focused on the likelihood of elevated spread as the weather turns colder in the late fall and early winter. The timing could coincide with the normal flu season, a confluence that could tax hospitals and medical care workers beyond current limits.

Could a football season continue through those events? Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases Institute, has his doubts.

"If there is a second wave, which is certainly a possibility and which would be complicated by the predictable flu season, football may not happen this year," Fauci told CNN earlier this month. Dr. Allen Sills, the NFL's chief medical officer, said in a statement that Fauci had identified important issues that the league and union continue to address. Regardless, the projected timing of this complication lands well before the end of the NFL's regular season.

"In the context of the NFL calendar," Binney said, "I definitely think it's more likely that you'll be able to start the season than finish it."

That would put the NFL in the same position as spring and summer sports that either had to halt play in midseason or delay the start of the season. But the NFL, based on the fortuitous timing of its season, could benefit from months of prep time. Binney has advocated for the NFL to follow a "home market bubble" approach, which would largely sequester players and coaches in a local hotel for the duration of the season while subjecting them to multiple tests per week. That strategy might seem extreme at the moment, Binney said, but could prove necessary to keep the season going in November and December.

Manage inevitable roster openings

NFL teams spend all year trying to prevent, mitigate and rehabilitate player injuries. Those efforts will take on a new dimension in the pandemic era, and there is a need for league-level intervention to handle infections and potential quarantines.

At a basic level, the NFL must ensure that each team has enough healthy players, at the right positions, to play credible games for 17 weeks. That almost certainly means an expansion of practice squads from the current limit of 12. It could also lead to a separate roster classification for players who are sidelined by the coronavirus, whether they tested positive, are showing symptoms or are quarantined. Otherwise, coronavirus-afflicted players would need to be carried on the 53-man active roster or placed on injured reserve, from which teams can activate only three players per season.

A more radical idea is to emulate the "Team 9" construct introduced during the XFL's shortened 2020 season. The idea was for a group of 40 players to practice together in a central location during the season, giving the XFL's eight teams a pool of healthy and presumably well-conditioned injury replacements. During the league's five-week season, 23 members were allocated from Team 9 to active rosters. Those players could get infected themselves, of course. But the NFL would have far more control over their social interactions using this concept than it would over players that teams individually sign off the street.

Coaches are also considering preemptive measures such as quarantining a healthy quarterback. Buccaneers coach Bruce Arians told the Green Light Podcast with Chris Long that he might keep his No. 3 quarterback away from the rest of the team to ensure the availability of a healthy passer who knows the offense and can start on short notice.

Eliminate incentive to hide illness or play through symptoms

In sports, we often hear about the difference between being "hurt" (in pain) and "injured" (loss of function). The truth about football is that players are incentivized to push through both. The vicious nature of the game ensures that nearly all of them will encounter an ailment of some degree during the season, but their non-guaranteed contracts leave them vulnerable to losing their jobs if they can't play.

It's reasonable to assume that most individuals will promptly report symptoms and follow protocols to minimize spread. But the unforgiving nature of the NFL's play-for-pay structure leaves open the possibility that someone will not. Unless the league requires daily coronavirus tests, which seems unlikely, it would take only one bad decision to initiate a spreading event.

That is only one of several sensitivities that the NFL and the NFLPA must address before training camp begins. The NBA, for example, has made exceptions for players who are at higher risk because of preexisting health conditions: They will receive their salaries even if they skip the restart of the season. Meanwhile, players who opt out for other reasons will have their pay docked by 1/92.6th for each game missed, up to a cap of 14 games, but not totally withheld.

"From an ethical standpoint," Heider said, "the system is not a level playing field. You could see young players particularly vulnerable, and maybe considered expendable, because it's not like they have $20 million in the bank already. It will be fascinating to see how that is dealt with in football.

"I think the public already has a heightened acceptance of risk for football players. But if something goes really wrong, where will public opinion go?"