Last Tuesday, the N.B.A. and its players’ union tightened their coronavirus protocols — mandating that players spend at least the next two weeks almost exclusively at home or at their hotels on the road when not playing basketball.

Three days later, the Washington Wizards held a news conference saying that six of their players had tested positive for the coronavirus and that the team did not have enough players to practice. That same day, Karl-Anthony Towns, the Minnesota Timberwolves star whose mother died of Covid-19, said that he, too, had tested positive.

Almost one month into the season, the N.B.A. has struggled to contain the coronavirus while playing outside of the restricted campus at Walt Disney World in Florida where it finished last season. Stars have been sidelined. Several teams, including the Wizards, Boston Celtics and Phoenix Suns, have postponed multiple games. Some, like the Philadelphia 76ers and Miami Heat, have taken the floor with skeleton crews, missing most of their top players because of contact tracing. More than 40 players have tested positive since training camps began in early December — 27 of them in the past two weeks. Only nine of the league’s 30 teams have not had a game postponed at least in part because too many of their players could have been infected.

And starting Wednesday, team security were to be stationed at midcourt before and after games to remind players not to hug each other.

The protocol shifts signal the difficulty in trying to play a contact sport indoors during the winter, when health experts said the pandemic would be at its worst. The N.B.A. was praised for being among the first major sports leagues to stop play when the pandemic reared its head last March and for finishing its season in the summer. But now some are openly wondering whether the league should be playing at all.

Even so, the league remains confident that its health and safety protocols are strong enough to withstand the outbreaks and that the postponements won’t threaten the integrity of its season. The players’ union declined to comment.

“I think it’s in line with where we thought we could be given how serious the pandemic was getting,” David Weiss, a senior vice president of the league, said of the postponements in an interview.

He added: “This exact time period is when we thought it was going to be difficult.”

The N.B.A. only scheduled the first half of its season, which was shortened to 72 games from the usual 82, in part because it predicted some postponements. In nearly 160 pages of protocols sent to the league’s 30 teams before the season, the N.B.A. said it was “likely” that some players and personnel would test positive and that it “may be necessary” to later modify the guidelines.

“Your protocol is only as good as the people are able to follow it,” said Dr. Cindy A. Prins, an epidemiologist at the University of Florida. She said not being in a bubble, as the league was during the summer, matters more than whatever the rules may be.

“The protocols could be great,” she said. “They’re relying, though, on individuals again. But now they’re relying on individuals with a lot less oversight. And they’re relying on people to understand what puts them at risk in getting Covid. We’re not good at that. I think we’ve proven that as a country.”

George Hill, a guard for the Oklahoma City Thunder, told reporters last week in response to the tighter protocols: “I’m a grown man, so I’m going to do what I want to do. If I want to go see my family, I’m going to go see my family. They can’t tell me I have to stay in the room 24/7. If it’s that serious then maybe we shouldn’t be playing. It’s life. No one’s going be able to just cancel their whole life for this game.”

The league’s contact tracing protocols, positive tests and injuries have at times left several teams without the minimum eight players required to compete. Those who test positive must isolate for at least 10 days or test negative twice more than 24 hours apart. Exposure to someone who has tested positive may also require a quarantine, depending on the setting and timing of the interaction. The N.B.A. uses the Centers for Disease Control and Prevention’s guidelines to define close contact as being “within six feet of an infected person for a cumulative total of 15 minutes or more over a 24-hour period” in the two days before a positive test or the appearance of symptoms.

Dr. John DiFiori, the N.B.A.’s director of sports medicine, said in an interview that while exploring the causes of the spread, the league found common transmission points, like car-pools without masks and shared meals.

“Our players and team staff all have families,” DiFiori said. “Some of them have children. Some of them go to school. And they go out into the community. We’re all subject to the same sorts of potential risks that anyone else is.”

In one case, for a team that had three players infected at the same time, the N.B.A. discovered that two of the teammates shared a meal and a car ride, and that the third teammate acquired a separate strain of the virus.

“It can be very hard to discern oftentimes the sources of introductions,” Weiss said. But, he added, the league had mostly found that the virus was being introduced outside team environments. Players are asked to encourage their family members and friends to adhere to the league’s protocols about avoiding risky behaviors and situations, like large indoor parties.

No team has been affected more than the Wizards, who haven’t played since Jan. 11 after postponing five games. In the days before their players tested positive, Washington had played the Celtics, Sixers, Heat and Nets — all teams with at least one player who had tested positive or been exposed to the virus. The league’s position is that playing in a game with a positive player does not, by itself, constitute close contact because players typically do not spend 15 or more minutes near any single other player. The league uses cameras to track how close players are to each other during games and for how long.

Tommy Sheppard, the general manager of the Wizards, told reporters last week that he was not sure of the source of his team’s outbreak. But he suggested that it might have spread because of on-court play.

“We have players that are out on the floor unmasked during the games,” Sheppard said. “That’s an obvious thing. They have exposure to each other. Sometimes, on the bench, players will put their masks down, talk to each other, things like that.”

He added: “But the fact is it hasn’t jumped a wall. It hasn’t extended past players. It kind of makes you at least, common sense, it would lead you to believe that maybe it’s happening because it’s contact out on the court or what not.”

On Monday, a Wizards spokesman confirmed reports that a staff member had also tested positive. Dr. DiFiori said that the league was still investigating the source of the outbreak.

Dr. Prins, who reviewed the protocols for The New York Times, noted that in defining close contact, the N.B.A. included a quote from the C.D.C. that said that the transmission from an infected person is based on several factors, including whether they are “likely to generate respiratory aerosols.”

“Well what do we think is happening on the court?” Dr. Prins said. “This is not two people sitting across from each other for 10 minutes and they haven’t even been talking or anything. These are people who are breathing hard and calling to each other on the court. I think it is very likely that they are generating a lot of aerosols. For me, I would want a very conservative definition of close contact here.”

One solution may present itself in the coming months. On Tuesday, N.B.A. Commissioner Adam Silver said during a live event with Sportico that there had been “discussions” about players getting vaccinated as part of a public health campaign.

Some officials, Silver said, “have suggested there would be a real public health benefit to getting some very high-profile African-Americans vaccinated to demonstrate to the larger community that it is safe and effective.”

Silver has also said several times that he did not want N.B.A. players to get vaccinated ahead of those most at risk. He said on Tuesday that players would get vaccinated only if public health officials deemed it the right time.

So for now, this appears to be the reality for the N.B.A. On Wednesday, the league announced its 16th postponement of the season and 11 new positive tests over the past week.

“What we’ve learned and it’s not a surprise is that the pandemic affects everyone associated with the N.B.A. just like it affects the U.S. population and the world,” DiFiori said.