Monday Night Football fans were shocked when Bills safety Damar Hamlin went into cardiac arrest on the field.

After making a tackle on Tee Higgins, Hamlin collapsed from an abnormal heart rhythm called ventricular fibrillation. He suffered this due to receiving a hit in the perfect spot to cause the abnormality.

Doctors from the University of Cincinnati say what Hamlin may have experienced was probably due to a condition called commotio cordis–a rare phenomenon that causes the heart to stop from a sudden blunt impact.

“It’s hard to tell whether it was a direct hit to the chest or maybe even an underlying health condition we don’t know about, but the hit to the chest is our best bet,” school nurse Natalie Kuhn says.

Hamlin was put into an induced coma and given oxygen due to the lack of blood in his lungs.

“There are injuries that happen in sports, but it’s rare to have something (that) incredibly serious (that quickly),” said Dr. Timothy Pritts in a statement. Pritts is a medical physician at the University of Cincinnati.

After two weeks of improvement, Hamlin has been allowed to continue his recovery at home.

“On behalf of our family, we want to express our sincere gratitude for the love and support shown to Damar during this challenging time,” Hamlin’s family said in a statement. “We are deeply moved by the prayers, kind words and donations from fans around the country.”