The sport has helped demonstrate how the novel coronavirus spreads and incubates; its potential damage to the cardiovascular health of young and healthy people; and how stringent testing and isolation protocols must be to limit outbreaks. It has even offered a vivid glimpse of the social costs when co-workers disagree over health protocols.

There is a difference between what MLB has done and what the National Basketball Association, for example, is doing. The NBA has built a sequestered “bubble” away from the general population, testing players every day and tracking their movements. It’s done everything public-health experts might dream of doing to get through a short season with a small, well-resourced population.

But not everyone can live in a bubble. Baseball, with a larger population and longer season, more closely resembles the real world. That’s why the national pastime has generated lessons that anyone can apply as they try to square what we currently know about coronavirus with daily life.

Close Contact: The Case of the Marlins

Baseball’s first conclusion was hard-won: A high-five, a handshake or a hug might be enough to contract the virus.

It took 18 players on the Miami Marlins contracting the virus to reach this point, and for MLB to close a mile-wide loophole in its rules. MLB had initially effectively said that people were only at risk of contracting the virus if they had been within 6 feet of an infected person for 15 consecutive minutes, or coughed on—mirroring the definition of close contact given by the Centers for Disease Control and Prevention.

The Marlins proved within days that baseball needed to reconsider that “close contact” definition. One player’s positive test turned to three, then six, and then nearly two-thirds of the roster. With every-other-day-testing and a lag of up to 48 hours before results came in, the virus had ricocheted through an entire clubhouse, and the team that eventually returned to playing was hardly recognizable as the Marlins at all.

Soon after, the league updated its protocols to make clear that “close contact” requiring isolation included “certain physical contact that is more likely to pass secretions,” otherwise known as handshakes and hugs. The Marlins, meanwhile, have somehow played well enough in spite of everything to be in playoff position.

Incubation Periods: The Case of the Cardinals

Epidemiologists say the virus can have an incubation period of anywhere from two to 14 days, which is why people are told to quarantine for that length of time if they’ve been exposed. The St. Louis Cardinals showed that if exposed people get on a plane or share a locker room with others early in that window, the virus can spread easily.

This case study began at the end of July, when two Cardinals players learned they had tested positive after they had flown with the team from Minneapolis to Milwaukee. Their July 31 game against the Brewers was postponed. A new round of testing began. The players were ordered to isolate themselves in hotel rooms. A day later, new tests yielded positives for another player and three staffers. Two days after that, on Aug. 3, a total of seven players and six staff had tested positive. None of the games happened.

But on Aug. 4, the team president said the Cardinals were ready to travel after multiple days of negatives. The team flew back to St. Louis on Aug. 5 and resumed light workouts. That was a mistake. There were three more positive cases on Aug. 7 from samples taken over the previous two days.

Some epidemiologists think the period of up to 14 days recommended for quarantine after exposure may be too long, since the likelihood of the virus waiting more than 10 days to manifest itself is very low. Research has coalesced around a median time from exposure to the onset of symptoms of four to five days. Either way, when the Cardinals waited three days to travel, they appear to have not waited long enough.

Hidden Heart Damage: The Case of the Red Sox Pitcher

It’s an open question how much young, healthy people without other medical conditions need to worry about the long-term effects of contracting the virus. That’s largely because there’s been no way to conduct any long-term studies of a disease identified mere months ago.

Boston Red Sox pitcher Eduardo Rodríguez was the first time many people heard about one frightening suspicion harbored by some physicians: that the disease could cause heart inflammation even in people who had only mild or moderate cases—and that inflammation could have fatal consequences if they tried to engage in vigorous activity.

Rodríguez, 27, has been diagnosed with myocarditis after heart screening and is out for the season. The inflammation is generally expected to subside over a period of months, allowing people to safely resume exercise with monitoring. Professional baseball, basketball and football protocols all require screening for heart damage.

That fear has now been cited as a factor in some conferences’ decision to pull back on college football in the fall, where it isn’t clear if every player can be screened. It’s also a fear held by some physicians about high school athletes and amateur marathoners.

Outdoors, At a Distance: The Case of the Phillies

Here’s a bright spot for MLB: There is no sign of an infected player spreading the virus to another team during a game. That’s also good news for hosts of outdoor parties where guests remain socially distanced from people who are not in their immediate households.

This was baseball’s big virology bet. It’s been proven right so far.

The Philadelphia Phillies were the team who played three games against the Marlins while the Marlins were taking tests that would later yield a mounting number of positive results. But day after day, as baseball held its breath, the Phillies’ tests yielded negatives, suggesting that inter-team transmission wasn’t going to be nearly as much of a problem as intra-team transmission. That has allowed the season to continue even if teams are stalled for days and whole rosters have to be turned over.

It also supports the argument that without close contact, there’s a relatively low risk of outdoor transmission. If your outdoor activity is akin to a baseball game—or even if it is a baseball game—what happens on the field is probably safe.

The Social Pariahs: The Case of the Indians

A lot of this rests on trust that people will adhere to agreed upon efforts to avoid contracting the virus, and trust that they’ll be honest about what they’ve done when asked.

The Cleveland Indians showed that people won’t always truthfully acknowledge their behavior—but also that there are severe consequences if they get found out.

Two pitchers on the team, Zach Plesac and Mike Clevinger, broke protocol after a Saturday night game in Chicago on Aug. 8. They sneaked out of their hotel, had dinner with a group and then visited a friend’s residence. MLB’s compliance officers caught Plesac when he returned, but not Clevinger. In a team meeting the next day, Clevinger didn’t admit to his whereabouts and wound up flying back to Cleveland with the rest of the team, potentially exposing everybody.

When the other Indians players found out, they were furious, ultimately prompting team management to demote Plesac and Clevinger to the minor-league complex. At Monday’s trade deadline, the Indians traded Clevinger, one of the top pitchers in the American League, to the San Diego Padres.

Nobody on the Indians ever tested positive. The important lesson was how angry people get if they find out that anyone has broken the rules established by a group (and that this happens with some frequency).

The Right Amount of Testing: The Case of the Reds (and the Mets and the A’s)

It seems the lessons baseball has learned from the outbreaks on the Marlins and Cardinals have already paid off. Since then, three teams have had a day in which they reported at least one positive test. Each time, the virus seemingly stopped there and didn’t spread throughout the rest of the clubhouse.

It started with the Cincinnati Reds. After a Friday night game against the Pittsburgh Pirates, they abruptly pulled outfielder Nick Senzel off the field. The team later announced one positive test without identifying the person but subsequently put Senzel on the injured list without providing a reason. (Players who test positive for the coronavirus are only identified if they give permission.)

The Reds had one comfort: Players had been tested that morning, and the results that included a positive test had arrived on the same night. It allowed the Reds to remove the positive person from the baseball population much faster than the Marlins and Cardinals had been able to.

Baseball’s testing regime was originally designed for testing every other day, with the results lagging up to 48 hours, against a packed schedule of games. Three days could pass between the time an infectious player took a test and learned of the result. His team was all but guaranteed to have played at least one game in that time—and maybe hit the road, too.

Baseball has added testing providers and increased the frequency of testing since the Marlins mess. The turnaround time from test to results significantly reduced the length of time the Cincinnati players might have been unknowingly exposed to a player who was infectious.

MLB also started postponing more games when positive tests emerged so it could attempt to halt outbreaks in their tracks. The Reds’ games were shut down for four days, during which time they registered no new positives.

A similar pattern has played out for the New York Mets and Oakland Athletics. The Mets had two positives. The A’s had one. No other positive tests popped up after the initial ones. The A’s returned Friday after missing four games.

There’s an applicable takeaway even for people who aren’t among the most tested people on earth. The length of time between taking a test and getting a result matters—and what happens between those two moments matters even more.