“The cells are, in a sense, stunned,” said Chris Nowinski, the chief executive of the Concussion Legacy Foundation. “You have this ongoing struggle for the cells to get the energy level back to normal. It’s an intense time frame for about five minutes.”

Umpires are just as vulnerable, especially the ones who set up in what they sometimes call the “kill zone” — the space directly over the catcher’s head or over his right shoulder during a right-handed hitter’s at-bat. That’s where umpires are most at risk.

“The moment you get hit, all you see is white, like a bright light,” the former umpire Jim Joyce said. “And believe me, it hurts like hell.”

Scott, who had four concussions in the last five years of his career, including two in the final ninth months, agreed.

“The first thing is, it’s loud, it’s like an explosion,” Scott said. “It’s like you almost go into shock. The last time it happened to me, my mind wasn’t on the next pitch. Instead I was thinking, ‘Is the next one the one that’s going to take me out?’ That’d never happened to me before. That’s when I knew it was time to get out.”

Unlike football or hockey players, who can retreat to the bench for treatment before returning to the game if they are not seriously injured, a catcher has only a few moments to decide if he can continue. Dangerous as it might seem, most do, falling back on a credo of toughness and commitment.