It was 8:55 p.m., the early stages of a hotly anticipated National Football League game, when it seemed as though a run-of-the-mill injury had interrupted the game.
“Another Bills player down,” said Joe Buck, the ESPN “Monday Night Football” announcer, not quite sure yet who was on the ground.
Mr. Buck soon realized the situation was far more dire. A replay showed that the Buffalo player, Damar Hamlin, had briefly stood up after the tackle and then collapsed, his body going motionless.
“We’ve all seen players go down,” Mr. Buck said in an interview on Tuesday. “We’ve seen players get up and then go down. But it was jarring to see the way he fell after he stood up.”
Within minutes, ESPN transformed from being a broadcaster of a football game to being at the center of a major and unexpected breaking news event. The question everyone wanted to know, including those at the sports network: What had happened to Mr. Hamlin, and would he be OK?
Several hours later, the Bills announced that Mr. Hamlin, 24, had gone into cardiac arrest after he tackled a Cincinnati Bengals receiver. On Tuesday, the team said he remained in critical condition in the intensive care unit at a Cincinnati hospital.
But in those early minutes, with millions watching and little information available, Mr. Buck was left trying to explain a possible life-or-death situation on live TV. He could see things had taken a terrible turn, and medical personnel were suddenly performing cardiopulmonary resuscitation on Mr. Hamlin. Mr. Buck knew little more than that, though.
“It was a nightmare,” he said. “It certainly was nothing that anyone is ever prepared for. You have all that hype and buildup and everyone can’t wait to watch this matchup, and in the snap of a finger it’s completely different. Football just goes out the window.”
For the next few hours, ESPN’s coverage of Mr. Hamlin would bounce to and from the broadcast booth, the field at the Bengals’ stadium, a nearby hospital, and studios in New York and Washington. On Monday night, ESPN suddenly looked like an episode of “Nightline” or a late hour on CNN, during a major breaking news story.
The network was cautious: There were few replays; there was little speculation about Mr. Hamlin’s health. Lisa Salters, the “Monday Night Football” sideline reporter, relayed only what she had seen: the Bills and Bengals coaches meeting and talking, players walking in and out of the locker rooms.
Not long after Mr. Hamlin collapsed, Mr. Buck pointed out that players on the field had been told they had five minutes to warm up and prepare to return to playing. ESPN’s footage showed the Bengals’ quarterback, Joe Burrow, making tosses. In a late-night news conference, the N.F.L. denied that it had considered restarting the game.
Mr. Buck said the five-minute warm-up information had come from John Parry, ESPN’s N.F.L. officiating analyst, “who is in an open line of communication with the league office in New York.”
“It is our obligation to give the information we are provided by the N.F.L. in real time as we get it,” Mr. Buck said. “That’s our job at that time. That’s all we can go with.”
On Tuesday afternoon, the network said that there had been constant communication with the league and that “we reported what we were told in the moment.”
“This was an unprecedented, rapidly evolving circumstance,” the network continued. “All night long, we refrained from speculation.”
About an hour after Mr. Hamlin fell to the ground, the “SportsCenter” anchor Scott Van Pelt took over the coverage from a studio in Washington, where the analyst Ryan Clark, a former N.F.L. player, joined him. From there, Mr. Van Pelt interviewed reporters who were at the hospital, as well as Ms. Salters from the field and Mr. Buck from the booth.
ESPN’s coverage showed the benefits of having a newsroom and analysts it can deploy when there is a stunning turn of events. The N.F.L. is beginning to strike deals with tech companies — YouTube just got the league’s Sunday Ticket package, and Amazon has “Thursday Night Football” — that don’t have those resources to fall back on.
In the broadcast booth, Mr. Buck received text messages from friends and family asking him what was happening on the field — perhaps there was something he knew that he couldn’t share on the air?
“I have absolutely no information,” Mr. Buck recalled saying. “All I can tell you is it’s serious and what I’m witnessing I’ve never seen before.”