“This is as personal as it gets,” Cunningham said. “I’m not hypothesizing here.”

Cunningham displays none of the Alzheimer’s-like symptoms that cripple many of those who are later found to have C.T.E., which can be diagnosed only posthumously. He said he recently went through testing that revealed no signs of brain problems.

He was in the prime of his career as a broadcaster, and most likely could have continued to make a comfortable living doing it for decades.

“You could put him on any game, and you knew he’d be rock solid and prepared and opinionated and smart and thoughtful,” said Lee Fitting, an ESPN senior coordinating producer who oversees college football coverage for the network. “He was always one guy you never worried about. He’s a consummate professional.”

Cunningham, too, spoke glowingly about ESPN and the job he left behind.

“I was being paid a really nice six-figure salary for not a lot of days of work, and a live television gig that, except for nonsports fans, people would beat me up to take,” Cunningham said. “I’m leaving a job that’s great. It’s not kind of good. It’s great.”

ESPN laid off dozens of on-air employees in April, but Cunningham was not among them. As the news broke that day, and Cunningham learned of colleagues losing their jobs, he made the decision that had been percolating in his mind for several years. He called and resigned.

At first, Cunningham told ESPN executives that he was leaving to spend more time with his sons, ages 3 and 5, and because of his workload as a film and television producer. He was a producer for “Undefeated,” a documentary about an urban high school football team, and has a string of projects lined up.