Damar Hamlin, a safety for the Buffalo Bills of the National Football League, went into cardiac arrest moments after tackling an opposing player during a televised game on Monday night.
Medical professionals were quick to render assistance to Hamlin and performed CPR on the 24-year-old player for several minutes before he was taken to hospital.
The incident has further raised concerns over the safety of American football, as players run the risk of injuries ranging from broken legs to brain-destroying concussions.
While it remains unclear exactly what happened, some medical experts believe Hamlin may have suffered from commotio cordis, a rare condition in which an impact to the heart causes it to stop.
“The heart is just centimetres below the surface and when you have trauma to that part of the chest, it disrupts the electrical activity and conduction in the heart,” explained Anthony Cardillo, an emergency medicine physician and chief executive of Mend Health.
While commotio cordis is extremely rare, it is not without precedent in contact sports.
“This injury and this event is not unique to football,” Dr Cardillo told The National. “It's unique to any sport where there's a potential for high velocity traumas to the chest and there are a lot of sports that could happen — lacrosse, baseball, soccer, hockey, et cetera.”
In 1998, National Hockey League player Chris Pronger collapsed on the ice shortly after taking a slap shot to the chest.
Pronger was revived and taken to hospital, where he made a full recovery and went on to play 12 more seasons in the NHL.
“Prayers that Damar Hamlin can have the same outcome that I was fortunate to have with my incident,” the retired hockey player tweeted.
American football has long been criticised for the toll it can take on players' health and safety.
On Sunday, quarterback Nick Foles started convulsing after taking a hard hit to his upper body. Foles was carted off the field and did not return to play.
There is also mounting evidence that the repeated head trauma many players incur throughout their careers may have lasting consequences.
A 2017 study by researchers at Boston University found chronic traumatic encephalopathy (CTE) in 99 per cent of brains obtained from former NFL players.
CTE is a degenerative brain disease that can only be diagnosed after death.
Earlier this season, Miami Dolphins star quarterback Tua Tagovailoa suffered a concussion that caused his fingers to splay during a game against the Cincinnati Bengals.
The hit on Tagovailoa came only four days after he took a hit that may have caused a concussion.
An investigation by the NFL and the Miami Dolphins into how Tagovailoa was cleared to play after the initial hit found that the Dolphins had followed the league’s concussion protocol.
The league and the NFL Player’s Association agreed to amend the rules so that a player who has shown ataxia or impaired balance will no longer be allowed to return to the game.
Dr Cardillo said he no longer feels comfortable letting his two young sons pursue football.
“I would have to say at this juncture, I would not promote my two boys playing tackle football. My wife certainly will not allow it after seeing what happened here,” he said.
