The NFL and medical experts have moved to quell the rampant speculation over what caused Buffalo Bills safety Damar Hamlin to go into cardiac arrest during Monday night's game in Cincinnati.
After making a routine tackle in the first quarter, the 24-year-old rose to his feet, then collapsed on his back as his body went limp. Hamlin received CPR on the field as players from both teams and millions of television viewers watched in horror.
On Wednesday, the Bills said Hamlin had shown "signs of improvement" but remained in critical condition at University of Cincinnati Medical Center.