From strict testing, masking and physical-distancing protocols in New York and California, to a full 40,000-seat stadium with almost no coronavirus restrictions outside Dallas.

These are the widely varying conditions sports fans can expect as large-scale spectatorship returns to big-league stadiums and arenas this spring. Americans are still getting infected with the coronavirus each day, and hospitalizations and deaths continue to add to the virus’s ghastly toll — but even the most Covid-weary cannot deny the life-affirming joy of root-root-rooting for the home team.

The question is, should you be rooting in person?

“The devil’s always in the details,” said Dr. Thomas A. Russo, chief of infectious medicine at the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo. But when masking and distance standards are closely enforced, “the risk is going to be low,” he said.

Fans were present on a very limited basis for some games at the end of last baseball season and in the N.F.L. season that concluded last month, and more recently for some N.B.A. and N.H.L. games. As of Friday, there have been no reports of community spread, but an argument can be made for waiting a bit before applying the face paint and heading out.

“We’re still going to have a moderate community burden of disease for another six to eight weeks,” Dr. Russo said. “After that, as we’re working on the vaccinations, I expect it to lighten. So baseball in July may be very comfortable,” he continued, “whereas Opening Day may be less so.”

This spring, the spectator policies of big-league baseball, soccer, hockey and basketball teams in the United States are governed primarily by the Covid-19 regulations of the 27 states where they are located, and the District of Columbia. The N.H.L. has extensive protocols for players, fans and buildings, and “none are independent of local, state, provincial or federal guidelines,” said John Dellapina, the league’s senior vice president of communications.

But that leads to wide variations in how many are able to watch a game at the stadium or arena — and the lengths to which they must go to get in. The best thing for prospective spectators to do is check on their favorite team’s website and see what they need to do for a ticket.

In New York, regulations currently allow 10 percent capacity at indoor sports venues — that translates to roughly 2,000 fans at Madison Square Garden for Knicks and Rangers games, 1,300 Islanders fans at Nassau Coliseum and 1,800 Nets fans at the Barclays Center — and 20 percent at outdoor venues.

Those fans must present evidence of a negative virus test taken within 72 hours of the game (at a cost of $60 or more); have that test result linked to their ID via an app, like the tech company Clear’s digital health pass or New York State’s Excelsior Pass; complete a health survey before entry; submit to a temperature check; and, once inside, wear a mask except when eating or drinking.

Outdoors, the same entry procedures will be in place, but with 20 percent capacity, when fans return to Yankee Stadium on Opening Day, April 1, and to Citi Field for the Mets home opener on April 8. (Both teams also say they will accept proof of full vaccination.) Gov. Andrew M. Cuomo announced the doubling of capacity for outdoor stadiums on Thursday, which means the Yankees can host almost 11,000 fans and the Mets about 8,400.

That will also hold true for the Toronto Blue Jays, who are likely to play home games in Buffalo’s intimate Sahlen Field starting in May or June if the U.S.-Canada border remains closed. At Sahlen, 20 percent capacity translates to about 3,300 fans.

Limited tickets and lots of social distancing

Of course, all of this is dependent on scoring a ticket. Season-ticket holders get first crack at seats, so resale sites are the best bet for the casual fan.

For some teams those secondary prices will be steep, given the limited supply, like the $260 nosebleed seat listed on Thursday for Islanders-Rangers at the Coliseum April 11. The cheapest resale price for a Red Sox-Orioles Opening Day ticket at Fenway Park (12 percent capacity) was put at $344. Currently, resale sites don’t even list tickets for Yankee Stadium or Citi Field until June.

New Jersey is allowing 10 percent capacity at Devils games indoors in Newark (about 1,800 fans), and 15 percent capacity for Red Bulls games outdoors in Harrison (about 3,750) when the Major League Soccer season starts on April 17. But unlike New York, no negative Covid-19 test is required. “If you buy tickets together, you can sit together, but otherwise, we have to spread apart,” said Gov. Phil Murphy of New Jersey.

Sports and health officials use algorithms to determine what percentage of capacity allows for six feet of spacing. For most arenas, that figure is 20 to 25 percent, so the Devils are well below that threshold.

In California, a color-coded system determined by local infection rates determines restrictions. Until recently, Los Angeles County was in the strictest purple tier, which would have restricted attendance to 100 fans at LA Galaxy and LAFC soccer games and Dodgers baseball games.

But the county has since moved to the red tier, which allows 20 percent capacity at sports venues. So when the Dodgers play their home opener on April 9, as many as 11,200 fans will be on hand at Dodger Stadium. Orange County also moved to red, which will enable 9,000 fans to turn out at Angel Stadium. So did San Diego County, giving the OK for 10,000 Padres fans at Petco Park.

And so it goes in a checkerboard manner across the country. The Colorado Rockies can fill their ballpark to just over 42 percent of capacity, or 21,000 fans who must wear proper masks. In Missouri, the St. Louis Cardinals can fill up to 32 percent of their stadium, and in Pennsylvania, the Philadelphia Phillies and Pittsburgh Pirates can fill 20 percent. But in Michigan, current regulations mandate that the Detroit Tigers admit only 1,000 fans, though the team says that figure could be increased.

In Oregon, state officials have not yet cleared the Portland Timbers men’s and Portland Thorns women’s soccer teams to allow fans into Providence Park. That’s also true for 13 N.B.A. basketball teams, though that number could shrink in the coming days.

Indeed, the N.B.A. has perhaps the most uniform leaguewide policy regarding Covid protocols. In the 17 arenas that currently admit fans, none are allowed to sit courtside and must be at least 15 feet behind team benches. Fans with seats within 30 feet of the court must present a negative Covid-19 test within 48 hours of game time or pass a rapid test on-site, and they are prohibited from eating.

The N.H.L. has also made rink-side adjustments after a few early-season outbreaks among players and officials in closed-door games. The plexiglass panels were removed from behind the team benches and the penalty boxes to promote air circulation. And at 18 of the 24 U.S. rinks that now or will soon allow attendance, fans are prohibited from sitting behind the benches and penalty boxes or along the glass.

And then there’s Texas…

Then there’s the Lone Star state, where Gov. Greg Abbott recently removed all Covid-19 restrictions.

The Texas Rangers took that as their cue to allow full capacity, all 40,518 seats, for the first three games at their new retractable-roof baseball stadium in Arlington — the first team in North America to do so. There will be no protocols beyond a mask-wearing rule at those two exhibition games on March 29 and 30 and the season opener on April 5. Subsequent games will be at less-than-full but still undetermined capacity.

Dr. Catherine Troisi, an infectious disease epidemiologist at UTHealth School of Public Health in Houston, said she would not recommend attending those first three games in Arlington.

“Will people keep their masks on, will they be drinking alcohol, will they be shouting, will the roof be open or closed?” she said. “There are so many risk factors. Even if you’re fully immunized, I’d advise against going.”

However, another Dallas team is showing more restraint. The N.B.A. Mavericks will continue to cap their attendance at about 25 percent capacity and require fans to complete a health questionnaire. “Nothing will change,” the Mavericks owner, Mark Cuban, said.

Golf fans, buoyed by the principle that outdoors is better when it comes to the coronavirus, are returning to PGA Tour events. Some 10,000 were expected for this weekend’s Honda Classic in Palm Beach Gardens, Fla. That’s 20 percent of maximum capacity.

But if it still seems like a lot of people on a golf course, don’t worry. The PGA Tour website reminds all spectators to make sure their temperature is under 100.4 degrees before they arrive and to maintain six-foot distancing.

And, as a final reassurance for those who simply must get out and watch a tournament in person, the PGA warns that “no autographs, fist bumps or selfies are permitted with players.”

Follow New York Times Travel on Instagram, Twitter and Facebook. And sign up for our weekly Travel Dispatch newsletter to receive expert tips on traveling smarter and inspiration for your next vacation.