John Urschel announced his retirement from the Baltimore Ravens in late July, two days after news broke that CTE had been found in 110 of 111 former NFL players who had donated their brains to science. It didn’t take a genius — like him — to do the math.

News media reports at the time said that the disturbing report was the reason Urschel retired at 26. But he says it had nothing to do with his decision. The timing, he says, was mere coincidence.

“It’s one of those things,” Urschel tells USA TODAY Sports, “where correlation and causation are not exactly the same thing.”

More:Ravens' John Urschel, 26, retiring from football after three seasons

More:Why try to convince Washington's Su'a Cravens to play when he doesn't want to?

He says he’d been thinking of retirement for months for a confluence of personal and professional reasons. Then, with training camp days away, he felt he had to make a decision — for the sake of the Ravens, where he was in the mix to start at center, and for his own sake, given the scale of his academic ambition.

Wednesday is the first day of his first fall semester at MIT, where he is a PhD candidate in applied mathematics. He has two spring semesters to his credit, but some courses are only available in the fall. Besides, he and his fiancée are expecting a baby girl in December and plan to marry next summer.

“I loved playing in the NFL, but it just felt like the right time to move on,” Urschel says. “I’m starting a family. Things with my PhD are starting to get more serious. … These are things I had been thinking about for a long time."

He’s been thinking about CTE for a long time, too. USA TODAY Sports spent a day with him in 2013 before his senior season at Penn State, where he’d already earned his undergraduate degree and a master’s degree, all with a 4.0 GPA. That day he spoke to a group of incoming freshmen committed to pursuing doctoral programs. They asked him about concussions. The unspoken context: Your brain is your ticket. Why put it at risk?

Urschel told them risk is part of playing sports and he accepted it. He’s been giving versions of that answer for years, including in a column he wrote for The Players’ Tribune in 2015. There he wrote about how he gets the question constantly, from news media members and math peers and at the NFL Combine.

“Objectively, I shouldn’t” take the risk, he wrote, but he spoke about the addictive rush he gets from playing football. “I love hitting people.”

Now he’ll hit the books full-time. He says he’s happy he played three NFL seasons, including 40 regular season games and two in the playoffs. “That’s something I’m going to have for the rest of my life,” he says, “that not many people can say.”

Nor can many people say they have co-authored papers with titles such as A Cascadic Multigrid Algorithm for Computing the Fiedler Vector of Graph Laplacians. Urschel puts the gridiron in multigrid algorithms.

“During the NFL, I was pretty blessed,” he says. “I only had one concussion. It was a pretty bad one but I only had one. If I had more of them, I probably would have thought about it more.”

He was knocked unconscious in August 2015. He says it took him about three weeks before he could play and somewhat longer before he could tackle high-level math concepts again.

“It took time for my brain to get back to full mental speed,” he says.

Surely that concerned him.

“You know, I don’t know why, but it really didn’t concern me that much,” he says. But it greatly concerned “my mother, my girlfriend — all the main women in my life.”

That girlfriend is now his fiancée. They live near MIT, not far from the New England Patriots. Would Urschel take the call if the Pats had injuries on their offensive line and Bill Belichick beckoned? “Only if he’s calling for math help,” Urschel says.

The Patriots open the NFL season Thursday. The Ravens get underway Sunday. Urschel figures he was in middle school in Buffalo the last time a football season started without him. He was technically a member of a team when he was in eighth grade, he says, but his head was too big for the helmets “so I was sort of a glorified water boy, so I’m not sure that counts.”

He played football for the first time in earnest as a freshman at Canisius High School, a Jesuit prep school. His mother sent him there for academics, not athletics, but he blossomed in both disciplines. She wanted him to go to college at — wait for it — MIT, but he settled on Penn State over Stanford in part because he dreamed of playing in the NFL.

Urschel says he’ll probably watch some NFL games on TV this season, mostly the Ravens. He appreciates that coach John Harbaugh has called him twice since he retired just to see how he’s doing. He says that’s typical of the coach and the organization.

Urschel weighed 310 pounds in July. Now he says he wants to “get down to non-NFL-lineman weight.” He’s at 295 pounds with a goal of 240.

When he retired, Urschel issued a statement that said “there’s no big story here.” He didn’t mention anything about that report in the Journal of the American Medical Association. Still, that report became the story of his retirement in many media outlets.

“Next time I’d say call me first,” Urschel says. “But it’s very likely they did call me. I wanted to retire quietly. My phone, I swear I got over 100 calls the first day. For someone who doesn’t like a lot of attention, I was uncomfortable with that and I didn’t answer any of the calls.”

Urschel earned $1.8 million in three NFL seasons, according to Spotrac.com. “I try to pretend that I’m still like a broke grad student,” he says, “but somehow no one is buying that these days.”

He could buy lots of things but prefers to live frugally. He says doctoral degrees in his field can yield the equivalent of NFL rookie contracts in certain industry jobs. “But,” he says, “what am I going to do with more money?”

He’s planning instead on a career in academia, where he looks forward to the deep satisfactions of solving maddingly complex problems. As for the physical satisfactions of football, he finds he doesn’t even think about the game anymore.

“Here’s the thing,” he says. “I’m not much for looking back. I’m always looking forward in my life. And that is a nice way to live.”