NFL

Doctors say they are still unsure what caused Hamlin's collapse during the Monday Night Football game against the Cincinnati Bengals a week ago.

For the more than 350,000 Americans each year who suffer cardiac arrest outside of a hospital, the prognosis is not always an optimistic one. But quick action with CPR and a defibrillator can be key.

Physicians interviewed by AP say there's no evidence Damar Hamlin's emergency was caused by his vaccine status, adding that there's been no increase in cardiac arrests among vaccinated athletes.

Dorrian Glenn said there were some encouraging signs in Damar Hamlin's condition, such as doctors lowering the level of oxygen needed from 100% to 50%.

It involves the impact of a specific force to the chest at a specific moment in the cardiac cycle. One cardiologist told NPR that what happened to Hamlin was likely "a perfect storm of events."

A list of some in-game or in-competition medical events that either suspended or postponed the competitions in which they occurred:

LISTEN: The Bills said Hamlin had a cardiac arrest after a hit. NPR's Rob Schmitz talks to Dr. Christopher Madias of the Cardiac Arrhythmia Center at Tufts Medical Center, about the effects of the blow.

The Monday night game between the Buffalo Bills and Cincinnati Bengals was suspended after Bills safety Damar Hamlin collapsed on the field.

The NFL and players’ union said that the Miami Dolphins followed the league’s protocol after the injury to the quarterback, but the outcome of the case “was not what was intended when the protocol was drafted.”

It's a “broken system,” Hall of Fame coach Tony Dungy tweeted after Tampa's Cameron Brate was allowed to play Sunday before he was diagnosed with a concussion at halftime. It came days after a similar situation with the Dolphins' Tua Tagovailoa.