Wearing a face mask to the ballpark to watch your baseball team? What about hand sanitizer at every aisle that you have to use before going to your seat at an NBA game? Should there be temperature checks when entering the arena? And can fans say goodbye to high-fives, hugging and even group selfies?

There are going to be many new realities when live sports return after the coronavirus pandemic, in whatever capacity that looks like, according to experts.

Ronald Waldman, a professor of global health at George Washington University who has also worked for the Centers for Disease Control and the World Health Organization, said that first there will have to be "serious declines" in the rate of infection, and good estimates as to how widespread infection was.

"To think that things are going to get back to normal soon, it may be a mistake to think that things are ever going to get back to normal," Waldman said.

Sports at every level around the globe have been canceled or postponed since mid-March due to the spread of the coronavirus, known as COVID-19.

"Even though there is a lot of uncertainty right now, one thing is very certain: People's expectations are going to change and our awareness levels are going to change," said Joseph Allen, a professor of exposure assessment science at Harvard University. "I think people will be looking at the environment differently."

By the time sports do come back -- though Allen, like many other experts, admitted he isn't sure when that will happen and what it will look like -- we will have been already practicing social distancing for so long, something that was once maybe awkward to do before "will stay the norm."

Keeping people 6 feet or more apart helps minimize the person-to-person spread of coronavirus, according to the CDC.

Allen said sports have a "huge role to play" in the aftermath of coronavirus, and that includes being a model in their behavior and actions. Having every other seat or every two seats empty for fans or having hand sanitizer at more stations throughout a stadium are easy behaviors to change across every sport.

"That expectation will be there, too. It will be about perception, about how people do or don't feel safe going back into these crowded environments," he explained.

Allen studies building science and health science, and the role indoor-built environments play in human health. He's worked with some of what he calls the "worst-case buildings" and believes "any building can be made better." That includes operational changes and behavioral changes, for example.

Making those changes is imperative, as sporting events can be a breeding ground for the spread of the virus.

The average attendance during the 2020 season for an NBA game was between 15,000 and 20,600 fans. Home games at Dodger Stadium last season averaged 49,065 spectators. A Green Bay Packers game -- cold weather and all -- averages 77,845 fans at Lambeau Field. SEC college football games average more than 74,000 spectators per game. And more than 23,000 people pack into Arthur Ashe Stadium in New York City to watch Serena Williams, Novak Djokovic and other dominant tennis stars every summer in the US Open.

Whenever sporting events do come back and in whatever capacity, a majority of Americans may not be ready to jump back into attending just yet. Some 72% of Americans surveyed in a new poll out Thursday said they would not attend if sporting events resumed without a vaccine for the coronavirus.

"The risk of transmission to the crowd is real," said Andrew Peterson, a professor and sports medicine specialist at the University of Iowa. "Let's say there's a certain percentage of the population that is asymptomatic and can spread it: If you've got fewer people in the building, there's fewer people like that in that crowd. If you've got a small group of people, you can do some things to mitigate some of that risk. You'd be a little bit better about cleaning services and maintaining space -- in a big crowded stadium, that's nearly impossible to do."

A stadium or arena can be a petri dish for any type of virus, Peterson explained. But he added that sports teams and leagues have known this and have long dealt with the risk associated with close contact at games -- for example, mono in colleges, he said.

Sports returning in whatever form face challenges from the federal government. On March 15, the CDC recommended the cancellation or postponement of gatherings of 50 people or more for the next eight weeks. The White House has also advised against social gatherings of any kind of 10 or more people. That puts every single sporting event, at least in the U.S., on the federal government's list of not-going-to-happen-anytime-soon.

"The determination of crowd density and fan seating will be informed by knowledge we gain over the coming weeks as we get more information on testing and the immune response protection that may exist after recovery from exposure. It is too soon to say what it will look like," Doug Aukerman, director of sports medicine at Oregon State University and senior associate athletic director there, said.

When President Donald Trump said this past weekend that stadiums and arenas would reopen "sooner rather than later," California Gov. Gavin Newsom -- who has five MLB teams, four NBA teams, three MLS teams, three NFL teams, three NHL teams and the storied Rose Bowl and L.A. Coliseum in his state -- shot back and said he doesn't anticipate that happening for football games come fall. Santa Clara County chief executive officer Dr. Jeffrey Smith said Tuesday that he doesn't "expect to have any sports games until at least Thanksgiving, and we'd be lucky to have them by Thanksgiving."

So do Newsom and Smith have the right mindset?

"I do think some of these half-measures of rolling things out slowly, playing in empty stadiums, they do make some sense," said Peterson, who is also the Iowa Hawkeyes' head team physician. "Nothing's going to be perfect at first, but turning things all the way back on before this is gone in the community is going to be hard."

Peterson said rolling out sports in a controlled manner is the best way to bring them back.

"It would be nice for it to kind of roll out in either the isolated communities where we can monitor what it does [and] to do it with certain small leagues so we can monitor what it does," he said. "Worst-case scenario is fall rolls around, and all of a sudden you've got NFL stadiums of 60,000 people and college football stadiums of 100,000 people, and 'boom' all at once, they won't really have any good sense. It might be that you roll it out and everything goes smoothly and you can scale up pretty quickly and sports start to look more normal, but I think if you do the same thing everywhere and it's a big mass exposure, you might end up chasing your tail and having to pull back."

In addition to having easier access to hand sanitizer, Waldman agrees with limiting attendance in a way that would allow for two seats in between fans. People also congregate around concession stands and drink stands -- should those be open?

"The level of risk in the individual community needs to be determined. And I think that there are going to be, within every community of sports fans, there are going to be some who are more risk-takers and some more risk-averse," Waldman, the global health professor who has also worked with the CDC and the WHO, said.