Following the coronavirus outbreak that infected nearly half of the Miami Marlins' roster and prompted the temporary suspension of the team's season, Major League Baseball is encouraging players not to leave hotels in road cities except for games, mandating the use of surgical masks instead of cloth masks during travel and requiring every team to travel with a compliance officer who ensures players and staff properly follow the league's protocol, sources told ESPN.

The updated rules, outlined in a memo distributed to teams Tuesday, came as MLB investigates the cause of the Marlins' outbreak that has seen 16 players and two staff members test positive for COVID-19, according to sources. The Marlins' games through Sunday have been postponed, and the prospect of their season restarting Tuesday at home against Philadelphia remains in question.

Commissioner Rob Manfred defended the league's protocol in an interview with MLB Network on Monday and could further strengthen it in the coming weeks as the consequences of the Marlins' outbreak become clearer -- particularly regarding the scrupulousness of contact tracing. The league on Wednesday also postponed Friday's scheduled game between the Toronto Blue Jays and Philadelphia Phillies, the latter of whom played the Marlins on Sunday before the scope of the outbreak was clear. The game is set for Saturday, giving Philadelphia an extra day to assess whether the virus was transmitted by the Marlins to any of its players, sources told ESPN.

Nowhere does the 113-page protocol that governs the 2020 season explicitly address how the league would handle a coronavirus outbreak, let alone one the magnitude of the Marlins'. It offers neither a threshold of cases to shut down a team nor a scenario that would cause a pause in the season. For a document as detailed and pedantic as MLB's operations manual, the lack of specificity on literally the entire reason for its existence -- the presence of a global pandemic -- has been a glaring omission, multiple general managers said leading up to the season.

It also was intentional, with the league seeking flexibility in its actions. The virus' infiltration of the Marlins this week proved seminal, finally putting a number on the lowest figure baseball is willing to stomach without shutting down operations beyond the heart of an outbreak: 18 positive tests, including 16 players -- 48% of those traveling with the team.

From the moment MLB committed to holding its season outside of a bubble and sending hundreds of people on the road every day, this was, if not inevitable, then at least expected. And yet the volume of Marlins personnel with COVID-19 still shook league officials who had hoped outbreaks would top off at half that size. For all the rigor MLB took with its protocol, the virus beat it in one place on the season's first weekend.

The fallout is only beginning. The Marlins are sidelined for the moment, their return date unclear. They are currently assessing how to fill out a roster with a combination of players already in their organization and training at their alternate site in Jupiter, Florida, free agents and waiver-wire claims. The Phillies, who played them Sunday when only four players were known to be COVID-19 positive, are simply hoping their daily tests continue to return negative, as they have been for two consecutive days, according to sources. The Baltimore Orioles and New York Yankees, who were supposed to be playing the Marlins and Phillies, respectively, started a two-game series Wednesday against each other instead. This is pandemic baseball: A schedule is a schedule until it's not.

More important than anything in the short term is how baseball adjusts in the wake of its first outbreak. As much as Manfred stood behind the protocol Monday, and as clearly as the league on Tuesday highlighted that the previous four days found no positive COVID-19 cases among the league's other 29 teams, here is the truth: The rules meant to protect players and keep them safe could not prevent a spectacular outbreak.

The investigation is looking into a wide range of factors, from the team's in-stadium behavior -- mask wearing, social distancing and other protocol-suggested factors -- to the off-field activities of players and staff, according to sources. The league will especially probe the veracity of players going out at night in Atlanta during the Marlins' time in the city for preseason games against the Braves. However much the actions of those in the Marlins' organization might have tested the protocol by not adhering to it, what happened Sunday highlights gaps that warrant more attention.

Following the positive tests of starter Jose Ureña, first baseman Garrett Cooper and right fielder Harold Ramirez, the protocol called for contact tracing -- a look into which other players or personnel fell within Centers for Disease Control and Prevention guidelines of "close contact": being within 6 feet of an individual for about 10 minutes, according to a copy of the protocol obtained by ESPN.

Only one player, sources said, was in that category after contact tracing: starter Sandy Alcantara, whom MLB Network reported was among those to later test positive. The notion that just one player among a team traveling 33 would be subject to the close-contact protocol -- quarantine pending the results of a rapid coronavirus test -- struck officials from other teams as unlikely. All 30 MLB teams are required to staff at least one trained contact tracer, while the contact-tracing operation is overseen by the league.

Following Sunday's game, the Marlins were walloped by the news that testing had turned up nine additional positives -- seven players and two coaches. On Tuesday, tests showed four more positives on the Marlins, and they were informed of another Wednesday. Including catcher Jorge Alfaro, who tested positive Friday in Atlanta, the Marlins had 18 cases, prompting Manfred to pause their season Tuesday amid mounting questions of how the outbreak had been handled.

Some elements of the protocol are unlikely to change, including testing. Currently, on-field personnel, including players, are tested every other day via a saliva sample. The sample is sent to MLB's Utah lab, where it is typically processed within 36 hours. In the case of an outbreak, the lag in testing could be problematic. It's also not something likely to be solved, sources said, with the more rapid point-of-care testing. The sensitivity -- or how often a lab test generates a positive that accurately reflects the presence of the virus -- is higher in the saliva test than the point of care.

Larger changes in MLB's protocol could be near. With the league now having postponed games, there is precedent, sources said, for pausing play at the first sign of an outbreak. If it's evident a cluster could be forming, one official said, the league could stop play for one team to get a better sense of how penetrative the virus has been. Of course, with the virus' incubation period lasting up to 14 days, according to the CDC, it remains possible that even a stop in play could be too late to keep the virus from spreading in the clubhouse.

The adherence to protocol around baseball has been a point of contention, particularly whether all of its elements matter. Players have spent the first week of play spitting, high-fiving, dogpiling and, in the case of the Astros-Dodgers contretemps Tuesday, ignoring social distancing -- and, at least to this point, have stayed coronavirus-free.

The first extension of protocols in the memo tighten them anyway. While the league won't mandate an on-the-road quarantine, players and team staff will be highly discouraged from even going into common areas of the hotel. On buses, the compliance officer will arrange seating charts -- and, in some cases, separate groups of friends likelier to run afoul of the 6-foot rule, which the league is treating as sacrosanct along with the adoption of surgical mask use for all. The compliance person, who will be designated with rare Tier 1 credential status given to essential personnel such as players, managers, coaches and training staff, will submit reports and monitor hotels.

The Marlins will be the first test case for the compliance person's efficacy. The team remains in Philadelphia, where it has been since Friday and could remain for the foreseeable future. Currently, the Marlins' next series is scheduled to start Tuesday in Miami against the Phillies. If, instead, the Marlins play that series in Philadelphia, they could bus to New York to face the Mets, then head via bus to Buffalo, New York, where the Blue Jays plan to play their home games this season. In that scenario, the Marlins would not return home until their Aug. 14 series against Atlanta, though Miami-Dade County currently requires a 14-day quarantine for people coming into town from New York, further complicating matters.

Miami could make up the three games against Washington that have been postponed this weekend by scheduling two doubleheaders during future series and playing on their shared Sept. 17 off-day. How to make up their four lost games against Baltimore, an interleague opponent, could prove tricky, leading to the possibility the Marlins won't play a full 60-game schedule.

Philadelphia's doubleheader against Toronto scheduled for Saturday illustrates baseball's on-the-fly maneuvering. MLB could introduce seven-inning doubleheaders this weekend, a prospect first reported by The Athletic. During a season in which the playoffs are expanding from 10 to 16 teams, a runner starts on second base in extra innings and the Blue Jays play their home games in the United States, a seven-inning doubleheader would fit the odd, unpredictable -- and, most of all, fragile -- 2020 season that nevertheless marches on.