Houston Astros fans reach to catch a home run baseball hit by Texas Rangers left fielder Willie Calhoun (5) in the top of the first inning during the baseball game between the Texas Rangers and Houston Astros on May 13, 2021 at Minute Maid Park in Houston, Texas.Leslie Plaza | Icon Sportswire | Getty ImagesMask mandates are slowly subsiding after the Centers for Disease Control and Prevention revised its guidelines on Thursday. That could be good news for sports leagues, so CNBC talked to a couple of experts about what this means for fans who are antsy to get back to attending games in person.The CDC said fully vaccinated individuals can, in most cases, drop protective face wear and no longer need to stay six feet apart. Unvaccinated people still need to follow stricter guidelines, as they remain at risk.”If you are fully vaccinated, you can start doing the things that you had stopped doing because of the pandemic,” CDC Director Dr. Rochelle Walensky told reporters. “We have all longed for this moment, when we can get back to some sense of normalcy.”The CDC has been cheered and criticized for its decision.Professional sports leagues, including Major League Baseball and the National Basketball Association, have been operating under city and state capacity restrictions due to the pandemic. The leagues have advised clubs to take their mask mandate cues from local officials. Masks at games are still required, and that rule could remain in place.The new rules are good for business as pro sports leagues lure back more fans, helping the leagues recover from billions in losses. That should further support the already rich National Football League, as clubs such as the Dallas Cowboys want 100% capacity for the 2021 season.’Not a Get Out of Jail Free card’The CDC still advises people honor business guidelines when it comes to mask mandates. Indoor arenas are riskier than outdoor arenas if you’re not vaccinated. So, the NBA and National Hockey League may need to keep their guidelines in place as they get ready for their postseasons.Gil Fried, a professor of sports management at the University of New Haven, advised pro teams to remain cautious.”When you’re at an arena, you don’t know what other people have and if they are vaccinated or not,” Fried said. “I still wouldn’t go to a venue without wearing a mask.”Asked when leagues should drop mask mandates, Fried said: “When the numbers across the globe decrease.” He then pointed to the nationwide lockdown in Turkey as cases spiked to over 60,000 per day.”Turkey was doing very well and considered a model of success. And now they have gone backward in a short period of time,” Fried said.Also, consider the recent Covid-19 outbreak within the New York Yankees that occurred even though team members were vaccinated. On Thursday, a positive test sidelined Yankees player Gleyber Torres for at least 10 days per MLB rules. And the league reported 10 new positive cases on Friday.Fried said leagues shouldn’t move too quickly on dropping mask requirements.”I think it’s great news for things like in-person training, but it’s not a Get Out of Jail Free card that is going to make everything better,” Fried said of the CDC news.”If you move too quickly, that can be scary for people,” he added. “They have been shut down for months. Yes, they’re anxious to get out there and do things, but there are still a lot of scared people. That’s part of the psychological side.”Fans stand for the national anthem of the game between the San Antonio Spurs and Sacramento Kings on May 7, 2021 at Golden 1 Center in Sacramento, California.Rocky Widner | National Basketball Association | Getty ImagesArenas are safer than you thinkAt this point, it’s a greater risk for leagues to change protocols, since there are still liability concerns. And city and state officials still hold the keys to fans fully returning.On May 19, New York will allow 33% capacity for unvaccinated sections at Yankees and Mets games and will offer free vaccinations at games. The Knicks are operating at 25% capacity. Meanwhile, in Pennsylvania, the Philadelphia 76ers are planning to allow 50% capacity as the team enters the playoffs.At the league level, MLB plans to keep its Covid-19 advisory to teams in place. The NBA didn’t respond to CNBC’s request for comment on its plans following the CDC update.But Stephen Kissler, who studies the spread of infectious diseases at Harvard University, said indoor arenas are safer now than pre-Covid. During the pandemic, teams invested in disinfecting facilities, germ-killing technology and improved ventilation systems.”All of these things together don’t reduce the risk to zero, but they do reduce it to something a lot closer to the risks we take every day,” Kissler said.NFL clubs have allowed more people to gather at games after the league started the 2020 season with limited capacity. More than 20,000 people attended the Super Bowl in February. But that was outdoors. Asked about Covid-19 risk with fully vaccinated people at a sporting event indoors — and wearing masks — Kissler said chances are low.”One of the things I would have wished for with the CDC guidelines — and maybe arenas can think about too — is that for these mask recommendations, they should be tied to the prevalence in the community around it,” Kissler said. “If you’re vaccinated and wearing a mask, and somebody next to you is not, and the prevalence in the community is low, then I think odds of the person next to you being infectious and spreading it to you while you have on a mask and are vaccinated are extremely low.”Kissler said allowing 75% capacity at indoor sporting events would be acceptable as cases decline.”That side of caution makes a lot of sense — doing these things slowly,” Kissler said. “But we’re entering a time when a Covid infection is no longer that scary of a thing anymore, which is great,” he added. “That’s what we’ve been pushing for this whole time.””I don’t think Covid is likely to go away. But with enough people vaccinated and with some level of immunity to Covid — where previously a Covid infection would have shut things down, I think we can raise the threshold a little bit,” he said.