This article has been updated to reflect the version that ran in print on Aug. 26.

Tyler Varga ’15, one of the most prolific rushers in Yale history and just the second program alumnus to play running back in the NFL since Calvin Hill ’69, retired from professional football this summer after just one season with the Indianapolis Colts.

Varga, whose rookie season ended late last September due to a severe concussion, initially indicated an intention to return to Indianapolis for the 2016 campaign. He participated in offseason workouts, but on July 26, the first day of Colts’ training camp, he was placed on the “reserve/did not report” list and was moved to the “reserve/retired” list later that day.

“He just decided that he wanted to move on with his life, and the risk of another traumatic injury was too great,” Joe Linta ’83, Varga’s agent, said. “He knows the career and life he’ll have off the field, and he didn’t want to take any more risk.”

Linta confirmed Varga’s retirement on July 26, adding that the decision whether to return for a second year had been weighing on the running back for the weeks preceding his announcement.

Varga’s concussion, which occurred on an onside-kick play during a game against the Tennessee Titans, left him dizzy, confused and fatigued for months after the hit occurred. He was placed on injured reserve two weeks later, eventually returning to Yale in the spring of 2016 to intern at the Yale Investments Office.

“It was a really tough stretch for Ty last fall, when the concussion happened,” Yale head coach Tony Reno said. “He was here [at Yale] last spring, and he was really shaken for about four or five months from the hit. It was one of those weird collisions that hit him just right, and I said to him, ‘Hey, that’s why you came to Yale.’ It’s the dream of every kid who walks in the door here, to further their career in the NFL, but if it doesn’t happen or if it’s taken from them, they have a great degree to fall back on.”

That great degree — one in ecology and evolutionary biology, in Varga’s case — came in use this fall. When the Colts diagnosed him with a concussion, one of the team doctors offered medicine to help him recover. Varga, an aspiring orthopedic surgeon, declined to take the pills, as he was not familiar with them. He consulted other doctors, all of whom told him to not take the drug.

He recounted this experience, as well as the lingering effects of his symptoms, in a May feature in the Indianapolis Star.

Sometimes, Varga said, he questioned if he would be able to play football again, or ever fully recover.

“I’d be lying, anybody would be lying, to say that wasn’t a thought that crossed my mind,” he told the Star. “I just remember thinking, ‘Thank God I went to Yale.’”

In his three regular-season games in Indianapolis, Varga picked up 151 yards on six kickoff returns and 20 total yards on one rush and one reception.

The Kitchener, Ontario native graduated from Yale as one of the most accomplished football players in school history. In three seasons, he racked up the fourth-most rushing yards and third-most rushing touchdowns in school history. After his senior season, Varga earned Ivy League Offensive Player of the Year honors.