St Mirren fans with face masks during the Ladbrokes Premiership match between Celtic and St Mirren at Celtic Park on March 07, 2020 in Glasgow, Scotland. Alan Harvey | SNS Group | Getty Images

The sporting world is feeling the weight of the COVID-19 outbreak that's spread from China to most countries around the world, infecting well over 100,000 people and killing nearly 5,000 globally so far. This week, few industries were left untouched by the virus, which the World Health Organization has officially declared a global pandemic. The outbreak sent global stock markets spiraling, the U.S. implemented sweeping travel restrictions on European countries and companies have been forced to cancel conferences around the world. Cities and countries have issued quarantine orders, shuttered school districts and banned large gatherings in an attempt to curb the spread of the fatal virus. And now, sports leagues are ceasing competition, including all four major and active U.S. leagues. Marty Conway, an adjunct professor at Georgetown University's McDonough School of Business, called the past two days of reckoning throughout sports "unprecedented." Conway, who spent time at AOL and served as a special advisor to former MLB Commissioner Peter Ueberroth, said the coronavirus' impact on sports is "like a combination of 9/11 and when Magic Johnson was diagnosed with HIV." "In the Magic experience, from what I recall, there was just so much uncertainty and the ability to comprehend what does this mean for players, fans, officials — people that would come in contact with someone with HIV," Conway said. "And there was enormous uproar, obviously, pre-social and digital media. But it was enormous." He said it's that element of uncertainty about COVID-19 — as well as the potential severity of it — that makes this unprecedented in U.S. sports. In the U.S., the virus has infected more than 1,701, according to Johns Hopkins University, and killed at least 40. "And then you had the post-9/11 conditions when everybody's question was: 'What's the right thing to do?' Is the right thing to play or not to play?" he said. "That's why, for me, this was unprecedented, because you had such an unusual mix of ingredients, never before coming together. This is truly the 'Black Swan' event for sports." Here are some of the leagues that announced disruptions this week:

NBA suspends season

The seats are empty at the Amway Center in Orlando, home of the NBAs Orlando Magic, on Thursday, March 12, 2020. The NBA has suspended the season due to the coronavirus. Stephen M. Dowell | Orlando Sentinel | Getty Images

The National Basketball Association on Wednesday night suspended its season indefinitely, opening the floodgates of league decisions announced Thursday. "The NBA is suspending gameplay following the conclusion of [Wednesday night's] schedule of games 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 decision came after a Utah Jazz player tested positive for COVID-19 shortly before the team was to play the Oklahoma City Thunder on Wednesday. That game was canceled close to the scheduled tipoff. Fans already in attendance were told by an official on the public address system to leave "due to unforeseen circumstances."

NHL suspends season

The National Hockey League announced Thursday it was immediately suspending its 2019-2020 regular season. "Our goal is to resume play as soon as it is appropriate and prudent, so that we will be able to complete the season and award the Stanley Cup," NHL commissioner Gary Bettman said in a statement. Bettman said there is a concern "that some members of the NHL community would test positive at some point." The Canadian Hockey League also said Thursday it was suspending play in all three of its regional leagues.

US soccer takes a hit

Major League Soccer announced Thursday the immediate suspension of all games for 30 days. MLS Commissioner Don Garber said all clubs were "united" behind the decision, adding that it is "in the best interest of our fans, players, officials and employees." The United Soccer League also followed suit, suspending play for 30 days. U.S. Soccer announced earlier Thursday the cancellation of all men's and women's national team matches in March and April.

MLB delays opening day

Major League Baseball announced Thursday it will delay opening day by at least two weeks and cancel spring training. Opening day was originally scheduled for March 26.

Minute Maid Park on September 10, 2019 in Houston, Texas. Bob Levey | Getty Images

"This action is being taken in the interests of the safety and well-being of our players, clubs and our millions of loyal fans," the statement said. The MLB was the fourth U.S. professional sports organization to halt its games

NCAA March Madness canceled

The NCAA said Thursday it is canceling its March Madness basketball tournaments — and "all remaining winter and spring" championships — after a flurry of conferences canceled their own tournaments earlier in the day. "This decision is based on the evolving COVID-19 public health threat, our ability to ensure the events do not contribute to spread of the pandemic, and the impracticality of hosting such events at any time during this academic year given ongoing decisions by other entities," the college athletics organization said in a statement.

A general view of a 'March Madness' logo is seen during practice before the First Round of the NCAA Basketball Tournament at Vivint Smart Home Arena on March 20, 2019 in Salt Lake City, Utah. Patrick Smith | Getty Images

CBS Sports and Turner Sports, which were set to broadcast the tournament said they are "fully supportive" of the decision. Some schools have gone further. Duke University, in addition to pulling out of March Madness, suspended all athletic competition, including practices, indefinitely.

World Cup Qualifiers postponed

World soccer governing body FIFA said Thursday it will postpone South American qualifying matches for the 2022 Qatar World Cup after a request from the region's football federation. Matches originally scheduled to take place between March 23 and March 31 are postponed, the organization said, adding that new dates will be discussed. A number of Latin America's top football stars play for European teams in countries that have seen significant cases of the virus and would have faced quarantines on their return to their home countries. "FIFA will continue to assess the situation in relation to COVID-19 and will decide whether further changes to the schedule of South American FIFA World Cup 2022 qualifiers are required," FIFA said, "always with the aim of protecting the health and safety of all individuals involved."

Golf world disrupted

The 2020 Masters golf tournament has been postponed due to the coronavirus outbreak, Augusta National Golf Club chairman Fred Ridley announced Friday. "Considering the latest information and expert analysis, we have decided at this time to postpone the Masters Tournament, the Augusta National Women's Amateur and the Drive, Chip and Putt National Finals," Ridley said in a statement. On top of that, the Players Championship golf tournament in Florida was canceled after the first round, the PGA Tour said late Thursday. The next three events have also been scrapped. "It is with regret that we are announcing the cancellation of The Players Championship and all events through the Valero Texas Open," the PGA Tour said on Twitter.

Brooks Koepka of the USA walks to on the 18th green during the PGA Championship at Bellerive Golf & Country Club on August 12, 2018 in St Louis, Missouri. Ross Kinnaird

The Tour sent players a text saying that the cancellation was due to a "rapidly changing situation" and that more information would follow. Shortly afterward it said in a statement: "We did everything possible to create a safe environment for our players in order to continue the event throughout the weekend, and we were endeavoring to give our fans a much-needed respite from the current climate. "But at this point – and as the situation continues to rapidly change – the right thing to do for our players and our fans is to pause."

European soccer suspended

All soccer matches in Spain's top division, La Liga, have been suspended for at least two weeks to curb the spread of COVID-19, the league's organizing body said Thursday. The league's statement said the decision came after Real Madrid put its team in quarantine, and that it had notified the clubs, the Royal Spanish Football Federation and the national sports ministry of the postponements. UEFA, the European governing body for soccer, announced the cancellation of two international matches following the quarantine. The organization said Thursday it will meet next week to determine the fate of future domestic and international competition. All soccer matches in England, including the top-flight English Premier League, will be suspended until April 4 due to the coronavirus outbreak, the league's governing body said Friday. "Following a meeting of shareholders today, it was unanimously decided to suspend the Premier League with the intention of returning on April 4," the organization said in a statement.

Boston Marathon delayed