The U.S. sports world faced a day of reckoning in confronting the coronavirus Wednesday as the NBA suspended its season after a player tested positive and the NCAA banned spectators from its marquee basketball tournaments, a dual shock that underscored the pervasiveness of the outbreak.

As public health officials and local governments escalated recommendations and orders against large gatherings, sporting events became the most prominent and most prevalent casualties, leaving Americans without one of their primary communal experiences as spring dawns amid a pandemic.

As the NCAA announced an unprecedented measure, the NBA became the first U.S. sports league to halt its season since the wake of the Sept. 11, 2001, terrorist attacks.

In a startling scene, Utah Jazz and Oklahoma City Thunder players left the Chesapeake Energy Center court in Oklahoma City shortly before tip-off after league officials alerted the teams of Utah center Rudy Gobert’s positive test.

After more than half an hour, the arena public address announcer made an announcement to the crowd.

“Fans, due to unforeseen circumstances, the game tonight has been postponed,” the public address announcer said. “You’re all safe. Take your time in leaving the arena tonight and do so in an orderly fashion. Thank you for coming out tonight. We’re all safe. … Please drive home safely. Good night fans."

“The NBA is suspending game play following the conclusion of [Wednesday’s] schedule until further notice,” the league said in a statement. “The NBA will use this hiatus to determine next steps for moving forward in regard to the coronavirus pandemic.”

The NBA’s stunning development overtook another momentous decision earlier in the day. NCAA President Mark Emmert’s announced Wednesday afternoon that all of the organization’s winter sports championships will be played in mostly empty venues. Widely referred to as March Madness, the men’s basketball tournament is one of the most popular events on the sports calendar, an enduring tradition that prompts alums and fans to make road trips, gather in bars during daylight hours and wager among friends.

Scheduled to begin Tuesday night in Dayton, Ohio, the games will take place “with only essential staff and limited family attendance,” Emmert said in a statement. The women’s tournament will begin similarly Friday and Saturday at 16 campus sites. Both still will be aired on television, but an eerie quiet will replace the usual raucous screams and flipping cheerleaders.

“While I understand how disappointing this is for all fans of our sports, my decision is based on the current understanding of how covid-19 is progressing in the United States,” Emmert said in a statement. “This decision is in the best interest of public health, including that of coaches, administrators, fans and, most importantly, our student-athletes. We recognize the opportunity to compete in an NCAA national championship is an experience of a lifetime for the students and their families. Today, we will move forward and conduct championships consistent with the current information and will continue to monitor and make adjustments as needed.”

Before Gobert’s positive test, the NBA’s Board of Governors held a conference call Wednesday to discuss the league’s coronavirus response options but reached no consensus as to whether games should proceed as normal, held without fans in attendance or suspended or delayed, according to people with knowledge of the call.

Major League Baseball has yet to face sweeping decisions about the fate of its hallowed Opening Day later this month, but the Seattle Mariners, Oakland Athletics and San Francisco Giants will be forced to postpone or relocate games scheduled at their home stadiums this month or play them without fans after government officials in those locales Wednesday banned large public gatherings.

Washington Gov. Jay Inslee (D) banned public gatherings of more than 250 people for the three counties that form the Seattle-Tacoma metropolitan area through the end of March, while San Francisco Mayor London Breed (D) set the limit at 1,000 for a period of two weeks. Oakland Mayor Libby Schaaf (D) also banned public gatherings of more than 1,000 in Alameda County.

The NHL mostly sat idle. The San Jose Sharks announced they would play home games without fans after Santa Clara County banned gatherings of more than 1,000 people. The league announced late Wednesday that it was “aware of the NBA’s decision tonight to indefinitely suspend its season due to a player testing positive for the coronavirus. The NHL is continuing to consult with medical experts and is evaluating the options. We expect to have a fourth update [Thursday].”

The decisions came on that a day that began with Anthony Fauci, head of the infectious diseases division at the National Institutes of Health, telling a congressional hearing that large gatherings should be prohibited.

The NCAA last week formed an advisory panel of experts and epidemiologists, and from there the NCAA’s outlook evolved rapidly. In an interview Saturday on CBS, NCAA Senior Vice President for Basketball Dan Gavitt said the NCAA is “definitively planning on running the tournament at all 14 sites with fans from the First Four in Dayton to the Final Four in Atlanta.” On Monday, one member of the panel told The Washington Post they agreed with Gavitt’s assessment.

Three days later, it dramatically altered its most lucrative and marquee event.

On Wednesday afternoon, Ohio Gov. Mike DeWine (R) said his state, which will host multiple tournament sites, would turn his strong recommendation from Tuesday not to hold indoor sporting events with spectators “other than the athletes, parents, and others essential to the game” into an order.

“The reason we’re doing the things we’re doing is we have the potential of becoming Italy,” DeWine said. “What we want to do is take action now to avoid that.”

Italy’s government placed the entire country on lockdown Monday. Eleven days earlier, it had fewer confirmed cases of coronavirus than the United States has now.

The Mid-American Conference closed its men’s and women’s tournaments, which started Wednesday at Cleveland’s Rocket Mortgage Fieldhouse, the same arena scheduled to host next week’s NCAA tournament games, to the public after DeWine’s recommendation. DeWine suggested legal reasons made the order an imperative for other leagues.

“Different organizations need an order from the government,” DeWine said. “It’s better for us to make their life easier.”

Before Gobert’s test introduced the virus into the players’ population, one probable consideration was insurance contracts. Most contracts include a “force majeure” clause that protect against unforeseeable events out of the insured’s control. But it is legally murky whether a government recommendation would trigger the clause, while an order certainly would. Leagues, teams and the NCAA will lose money regardless, but they could have lost more by following recommendations rather than orders.

As the NCAA made its announcement, some conferences moved ahead with tournaments as scheduled. The ACC held a game with a crowded arena in Greensboro, N.C., as Emmert’s announcement came out, and later said it would play two games Wednesday night with fans in attendance but would not allow the public in for the remainder of the tournament.

The SEC announced its tournament in Nashville would continue Wednesday night with spectators as scheduled, but that it would reevaluate Thursday. The Big Ten, which played tournament games with fans in attendance, announced later Wednesday that it would play the remainder of its tournament without them. The Big 12 said it would allocate each team in its event 125 tickets apiece, beginning with Thursday’s games.

Next week’s NCAA events will be broadcast as previously scheduled on CBS and multiple Turner cable channels.

“We support the NCAA’s decision to proceed without fans at the tournament venues,” the networks said in a joint statement. “We will continue with our plans to fully produce and cover the entire event.”

For first- and second-round sites next weekend, the arenas will remain the same. But for the four regional sites and the Final Four in Atlanta, Emmert told the Associated Press, the NCAA will seek to move the events from cavernous football stadiums to more intimate venues.

In the sports world, some of the biggest dominoes fell Wednesday, one in dramatic and shocking fashion. There probably will be more to come.

“This seems difficult for people,” DeWine said. “But we know what’s coming. We know what’s around the corner. … Everything looks the same, but it’s really not.”

Dave Sheinin and Samantha Pell contributed.