Buffalo Bills player Damar Hamlin is in critical condition after suffering cardiac arrest during a game on Monday night. The cause of the cardiac arrest is unknown, but it is suspected to be commotio cordis, a rare condition in which a blow to the chest can induce a dangerous heart arrhythmia or cardiac arrest. Responders administered CPR and defibrillation immediately and were able to restore Hamlin's heartbeat at the scene. His prognosis is currently unclear, but the quick medical response and his young age and good health give hope for a full recovery. No further updates on his condition have been released.