The football field becomes Tua Tagovailoa‘s quiet lawn when he walks on it. With that loose, easy stride, it’s as though he were moving across the freshly mowed grass of his own yard. The cheers and jeers of the crowds don’t seem to reach him. The excitement subsides around him as he strolls toward the center’s rump.

But this time was different. When Tagovailoa collided head-first with Buffalo safety Damar Hamlin‘s chest in the Dolphins’ second game of the season, the world stopped spinning. The quarterback lay there, dazed, his arms stiff in front of him like a boxer who just took the big one. The fencing response, they call it — a clear sign of fresh trauma to the brain.