It's a rare event called commotio cordis. It happened to an NHL hockey player in 1998. From the linked article below: "Commotio Cordis refers to the sudden arrhythmic death caused by a low/mild chest wall impact. Commotio Cordis is seen mostly in athletes between the ages of 8 and 18 who are partaking in sports with projectiles such as baseballs, hockey pucks, or lacrosse balls. These projectiles can strike the athletes in the middle of the chest with a low impact but enough to cause the heart to enter an arrhythmia. Martial arts is a sport in which a strike of a hand can also cause the heart to change it’s rhythm. Without immediate CPR and defibrillation the prognosis of commotio cordis is not very good. This condition is extremely dangerous with rare survival."It sounds like the most freakish of injuries. The hit to his chest that he took while tackling stopped his heart.![]()

Commotio Cordis | Korey Stringer Institute
Commotio Cordis refers to the sudden arrhythmic death caused by a low/mild chest wall impact. Commotio Cordis is seen mostly in athletes between the ages of 8 and 18 who are partaking in sports with projectiles such as baseballs, hockey pucks, or lacrosse balls. These projectiles can strike th ...

News article on Damar Hamlin with quotes from a cardiologist.

What to know about ‘commotio cordis’, the injury that potentially stopped Bills safety Damar Hamlin’s heart
When Bills safety Damar Hamlin collapsed on the field after a tackle on live television, William Gray, a Philadelphia-area cardiologist, turned to his wife and said, “that’s a serious problem.”