Exactly 100 days remain before the scheduled start of the NFL season. If the Houston Texans and Kansas City Chiefs actually kick off Sept. 10 at Arrowhead Stadium, they will produce one of the most significant moments in league history.

None of this country's major professional leagues has managed to resume play since the start of the coronavirus pandemic. The NFL and NFL Players Association have more time and less urgency than their cross-sport counterparts, but the issues -- testing, safety protocols, payroll adjustments and fan policies among them -- are no less difficult to resolve.

The NFL has been pledging an on-time start to the season for months, even while working on multiple contingency plans behind the scenes, a number of which were built into the regular-season schedule. One could push the Super Bowl to the end of February.

"As a league, and in partnership with the players' association, we will continue to prepare and to adjust where necessary," commissioner Roger Goodell said during a recent media teleconference. "I think this offseason has looked a lot different than it has in the past. We are proud that our key activities, such as free agency, the league year, the offseason programs and of course the draft, demonstrated that we can operate in new and innovative ways, so we are prepared for the 2020 season."

If the NFL season is truly to start Sept. 10, the league has a long agenda list for the next 100 days. Let's take a closer look, both on and off the field.

What is the status of team facilities?

The facilities began reopening on May 19 as state and local guidelines have relaxed. The first phase limited teams to bringing back no more than 50% of its non-field employees, for a total of up to 75 people in the building at any time. Coaches and players, other than those receiving medical treatment, were not part of that group.

The second phase began this week, as the league anticipated all facilities would reopen at some capacity. In a memo to teams, Goodell said last week that he anticipated allowing coaches to return by Friday. There is hope -- but no plan yet -- for the return of players before the NFL offseason ends June 26.

So what does that mean for teams' offseason programs?

The programs will remain virtual through at least June 12, at which point the league and the union will reevaluate national conditions.

That leaves a two-week window, from June 15 to 26, when the NFL could potentially allow players to return for on-field workouts. For scheduling purposes, teams have saved the one mandatory event -- a three-day minicamp -- for potential use in that time frame. But there is no guarantee that the NFL will be ready to utilize that time. And even if teams receive that authorization, it's possible that some will opt against a scramble to bring players from all over the country into the facility for such a short period.

"We've got to get this right," said Troy Vincent, the NFL's executive vice president of football operations. "We're coming out of phase 1, going into phase 2, and we have to assure the general public and our players that our protocol and procedures [work]. We can't miss. We just can't fail. So rather than saying, 'Yes, we're going to do this,' we have time. We have to be right. We are really taking a responsible approach on a daily basis. It's changing daily."

What is the significance of June 26? Could the offseason be extended to get more virtual work in?

By agreement with the players' association, via the collective bargaining agreement, the league limits both the amount and period of time that players can participate in offseason team workouts. This year, the latest day that teams can host player workouts is June 26, allowing for a monthlong quiet period before training camps open.

We've learned this year not to rule out unusual or unprecedented events, but an extension beyond June 26 would seem unlikely and almost certainly would be tied to an acknowledgement that the start of training camps would be pushed back.

So will training camps be pushed back?

That's impossible to predict right now. We don't even know how the offseason program will end! All teams have been instructed to plan an on-time start to camps in late July, but its ultimate timing -- and that of everything that follows -- is largely dependent on three key factors:

• The NFL's success in conceiving and implementing a health and safety protocol that minimizes the chances of infection and ensures quick action to prevent spread

• Agreement from the players, via the NFLPA, on that protocol and on any potential economic concessions

• Acquiescence from state and local governments in the localities that house NFL stadiums

What will the NFL's health and safety protocols look like?

Most of it remains in development, and part of it will be adjusted in reaction to trial and error from other leagues. We've gotten a few glimpses, including efforts to design a helmet visor that could limit the flow of virus through airborne particles.

Dr. Allen Sills, the NFL's chief medical officer, has made clear that the league should expect some personnel to be infected and said: "Our challenge is to identify them as quickly as possible and prevent spread to any other participants."

Sills also said that "certain important steps" in testing and testing availability must happen before the NFL has large-scale events. In other words, production and availability of test kits must increase to the point where the league can test all of its participants regularly and reliably without limiting the supply for the rest of the public.

"When we and the players' association feel that we are at a point of satisfaction with that science, then we'll be ready to move forward," Sills said.

Once everyone is comfortable on the science, the NFL and NFLPA will need to address a series of other important aspects of their coronavirus policy. While physical distancing is not possible during games, will practices be reorganized to limit proximity? Will players and coaches be quarantined when not at the team facility? Will rosters or practice squads be expanded to ensure a full complement of healthy players? What about players with underlying conditions, those in high-risk groups and those who have other personal reasons to stay away from the field?

Atlanta Falcons center Alex Mack, the treasurer of the NFLPA, told reporters he is more concerned about players getting infected while away from the team facility or stadiums.

"I think it comes down to how can you control when people go home," Mack said. "What they do, what the people at their home are doing. It's just the whole spiderweb effect of contamination that's hard to wrap your head around and kind of figure out. I guess the fear of the unknown, to me, concerns me."

In addition to the health of players, the NFL also must take into account the rest of its on-field personnel, from coaches to athletic trainers to game officials. The NFL has three head coaches over the age of 65 and a total of six who are at least 60 years old. And the average age of the league's game officials is 52, according to NFL Referees Association executive director Scott Green.

Let's back up: What did you mean earlier by potential economic concessions?

It's messy, and no one wants to hear about it amid record unemployment numbers around the country. But the experiences of the NBA and Major League Baseball, in particular, show us that the NFL's return to play is dependent on cooperation between owners and players on issues they don't always agree on.

Owners already have instituted some pay reductions and furloughs among off-field staffers. What will happen if they ask players to also take pay reductions outside of their collective bargaining agreement?

The league's salary cap addresses the question from a philosophical standpoint. Players would share in the impact of lower revenues in 2020 via a smaller salary cap in 2021. Would owners seek additional concessions? We would be fools to rule out the possibility.

Regardless, training camps won't open on time and the season won't kick off Sept. 10 without players' full cooperation.

Is there really a chance for fans to attend 2020 games?

Not every state has addressed whether it will allow professional sports this summer or fall -- or whether fans would be allowed to gather in significant numbers. But contingency planning includes the possibility of admitting a limited number of fans per game.

During an appearance last month on CNBC, Miami Dolphins owner Stephen Ross said: "I think there definitely will be a football season this year. [The] real question is, will there be fans in the stadium? Right now -- today -- we're planning to have fans in the stadium."

The Dolphins recently unveiled plans to limit crowds to as low as 15,000 people at Hard Rock Stadium, allowing them to maintain physical distancing within the 65,000-seat facility. Would the NFL allow some teams to admit fans if others are prevented by state or local regulations? The league hasn't yet said.

What about the rest of the NFL's offseason schedule?

Even after the end of the offseason program, teams can continue to work through existing individual contract situations, including signing their rookie classes.

July 15 remains the deadline for signing franchise players to long-term contracts. Otherwise, they must play the season under a one-year deal. In this unusual offseason, none of the 14 players tagged has signed new deals, a list that includes Dallas Cowboys quarterback Dak Prescott, Jacksonville Jaguars defensive end Yannick Ngakoue and Tennessee Titans running back Derrick Henry.

Isn't the Pro Football Hall of Fame induction usually in the summer?

Yes. At the moment it remains on the schedule. The annual Hall of Fame Game would be played Aug. 6, and the Class of 2020 would be inducted Aug. 8. But David Baker, the Hall's president and CEO, told USA Today that he is considering multiple contingencies, including pushing the ceremony to the spring or combining it with the 2021 induction.

What plans are being made by the NFL for game officials?

In most years, the NFL officiating department's annual July clinic would be especially busy. The department has new leadership that includes former coach Perry Fewell, now the senior vice president of officiating administration, and retired referee Walt Anderson, now senior vice president of training and development.

The clinic is likely to be held via video conference, according to Green. The NFLRA also is discussing contingencies for the season, such as whether it would make sense for officials to be assigned to games based on their home city to minimize air travel.

Here's another random issue to consider in the coronavirus era: Could whistles accelerate the spread of the virus? And if officials wear masks during games, how would they blow a whistle?

So when will we start getting clarity on all of this?

The NFL has followed a simple rule throughout the coronavirus pandemic: Maintain original schedules until they are no longer viable. So there is no reason to expect the NFL to make any imminent announcements about training camp or the season. For the most part, it has implemented its virtual offseason program in two-week increments. That's a good working understanding for how the rest of the summer could go.