Hamlin is one of the athletes who have had heart problems while playing.
A man fell to the ground after colliding with an opponent.
Medics said he had gone into cardiac arrest because his heart had stopped beating and he couldn't pump blood around the body.
It was necessary to resuscitate him on the pitch.
He is critically ill in the hospital.
The doctors are not sure of the underlying cause.
Something called commotio cordis is caused by blunt trauma.
A direct hit to the chest can cause the heart to go into a rhythm that is life threatening.
Blood supply to the heart muscle is cut off in a heart attack.
Major structural damage to the heart can be a result of blunt trauma.
It's not known if Hamlin has suffered any serious damage to his heart or what internal injuries he has.
Hypertrophic cardiomyopathy is a genetic disorder that can be fatal for young athletes.
There are no obvious warning signs that this is a serious underlying problem for individuals who have this.
It's a condition in which the heart is enlarged. It can be difficult for the heart to pump blood. There may be life threatening heart rhythm problems as well.
The news of Hamlin's collapse caused anti-vaccine activists to jump on it.
Athletes collapsing on the field was not a normal event according to the account promoting the anti-covid film. This pattern is becoming an inescapable one.
A number of anecdotal reports of athlete deaths have been collected by anti-vaccine activists.
There are about 100 to 150 sudden cardiac deaths each year during competitive sports in the United States.
Hamlin's vaccine status isn't known. Almost all of the players in the National Football League were protected against Covid.
He is not the only athlete who collapses in a big game. Christian Eriksen was close to death on the pitch at a Euro 2020 match.
The doctors used a defibrillar to shock his heart. An ICD is a small device that keeps his heart on track.
There was no history of a heart condition in his family and he was tested regularly throughout his career.
In 2012 a footballer named Fabrice Muamba collapsed on the field. There were 15 shocks.
It isn't always possible to save every life.
There are many different causes of sudden death in young people. They aren't very common.
Twelve people under the age of 35 die from sudden cardiac arrest in the UK every week according to Cardiac Risk in the Young.
No definite cause of death can be found in about 1 in 20 cases of sudden cardiac death and up to 1 in 5 young sudden cardiac deaths, even after an expert cardiac pathologist has examined the heart for structural abnormality.
An electrocardiogram test is a simple way to detect cardiac abnormality. If the electrical impulses are messed up, it can be revealed. It is possible to treat dangerous arrhythmias before they cause a big problem.
More about the topic can be found here.
If someone is, do it.
If someone is unconscious but breathing normally, call the emergency services and place them in the recovery position.
If someone is unresponsive and not breathing, then call and start cardiopulmonary resuscitation.
The additional reporting was done by Mike.