The Baltimore Ravens’ John Urschel raised eyebrows a few years ago when he published a research paper in Linear Algebra and Its Applications, a peer-reviewed math journal.

Now, after playing in the NFL for three years as a center and guard, Urschel, a native of Winnipeg, Canada, is retiring from his football career to focus on mathematics at MIT. His goal is to earn his PhD (he already has a bachelor’s and master’s in mathematics, both from Penn State).

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There are thousands of bright young American students in graduate school for math and thousands of professional football players, past and present — but there are very few people who have attempted to do both and to excel at both. Yet it’s no coincidence Urschel is attempting to succeed in two different fields on opposite sides of the spectrum. His work ethic is the key to his success.

“He works hard, all the time,” said Ludmil Zikatanov, a professor who has labored with Urschel on four of his nine papers, according to MIT Technology Review.

While the lineman has repeatedly described and emphasized his love of math, he was also quoted by The Washington Post as saying, “I love hitting people.”

Ravens Coach John Harbaugh said in a statement last week that he respects the player’s decision and that the team “appreciate[s] his efforts over the past three years and wish[es] him all the best in his future endeavors.”

On Friday, as noted by ESPN, “Urschel sent a text to The Undefeated’s Domonique Foxworth, who read part of it on ESPN’s ‘First Take.'”

The text from Urschel said, “I guess the biggest thing I’d want to say is that I’m excited to focus on my mathematical career full time. And to finally be at MIT full time. A place that I love so much. And when I really thought about it, it didn’t make sense to play this season, when the thing I’m most excited about is mathematics right now … But that I love the game, love football.”

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Interestingly, Urschel’s retirement announcement came just a few days after the release of a study further showing the link between football and CTE, a brain disease.

Related: A Single Season of Head Trauma May Change the Brain

Of the 111 former NFL players’ brains studied, 110 showed signs of CTE. The increased risk of brain problems later in life has caused many NFL players to hang up their helmets early — and Urschel is the latest example.