As Hamlin was rushed to the hospital, players on both teams were visibly upset leading NFL officials to postpone the game.
Millions of people online sent thoughts and prayers to Hamlin, hoping the 24-year-old would make a full recovery.
But with no known prior health conditions, why did Hamlin suffer cardiac arrest?
\u201cMy prayers are with Damar Hamlin.\n\nAs an arrhythmia specialist, I believe the blow to his chest during a certain period in the cardiac cycle triggered ventricular fibrillation, a condition called Commotio Cordis.\n\nIt is not associated with pre-existing heart damage or COVID \ud83d\udc89\u201d
People believe Hamlin went into cardiac arrest because the force at which he was hit in the chest disrupted his heart rhythm.
The condition called Commotio Cordis is rare but occurs in athletes that play sports like baseball, hockey, or football.
If a blunt force hits the chest while the heart is at a critical point in its cycle it can cause arrhythmia which can send the heart into cardiac arrest.
Commotio Cordis is not caused by heart disease or underlying conditions, it can happen to anyone.
Although Hamlin's official cause for cardiac arrest was not announced, people online speculated this was the case because it is often seen in sports.
\u201cDoctor @BrianSuttererMD Explains The Cause of Damar Hamlin's Cardiac Arrest :\n\n- What happened to Damar Hamlin has NO relation with any Vaccine \n\n- It's most likely a rare condition called Commotio Cordis which can be life-threatening\n\n#DamarHamlin #BillsMafia #Bills #NFL\u201d