BERKELEY — Cal team physician Dr. Casey Batten said Bears defensive end Ted Agu, who died Friday morning after a team training run, had experienced no health problems during previous workouts.

Agu, 21, was finishing a routine offseason run when he began “having difficulty” about 150 yards from the north entrance to Memorial Stadium, Batten said. Agu, a junior from Bakersfield, was talking while being taken by cart to the Simpson Center medical facility, where he collapsed and became unconscious. CPR was administered, and Agu was declared dead shortly after 7 a.m. at Alta Bates Hospital in Berkeley.

“This is certainly one of those tragedies, as we talked about to our football team today, no one can understand and comprehend,” Cal coach Sonny Dykes said at a campus news conference. “Ted was a very special young man.”

CBSSports.com reported that a source confirmed Cal knew that Agu had tested positive for the sickle cell trait, but Batten said he was not permitted to confirm it. Sickle cell screening has been mandated by the NCAA since 2010.

A Cal spokesman said an autopsy would be performed.

The CBS story said sickle cell trait doesn’t mean Agu died because of it or that blame should be placed on the university. But the story said that since 2000, sickle cell trait-related cases are the leading cause of death among NCAA Division I football players, with an overwhelming majority of those coming during offseason conditioning.

Agu came to Cal as a nonscholarship “walk-on” but was rewarded with athletic financial aid in March.

“He had a passion and energy for life that was contagious,” Dykes said. “He will be deeply missed. Our players loved him dearly.”

Agu was a public health major and a second-team Pac-12 all-academic selection in 2013. According to Stefano Bertozzi, dean of Cal’s school of public health, Agu had plans to study medicine.

“Ted demonstrated strong leadership skills, serving as an informal peer adviser for incoming freshman football players,” Bertozzi said in a statement.

That was backed up by members of the team. “Guy was incredibly smart would help me and the other younger guys whenever we needed it in the classroom,” tweeted freshman running back Jonah Hodges.

Reaction was swift and came from Agu’s teammates, former Cal players and opposing schools.

Tweeted Bears quarterback Jared Goff: “One of the nicest, most hard working, and joyful people to be around. You will be greatly missed. RIP Ted”

Condolence tweets also came from NFL stars such as Shane Vereen of the New England Patriots, Marvin Jones of the Cincinnati Bengals and Keenan Allen of the San Diego Chargers.

Also remembering Agu was former Cal coach Jeff Tedford, under whom Agu joined the team.

“It was mission accomplished 100 percent,” said Tedford, now the Tampa Bay Buccaneers offensive coordinator. “Not only did he earn a scholarship, but along the way he gained the respect and admiration of his teammates, which is far more important than football.”

UCLA coach Jim Mora, Bruins quarterback Brett Hundley and the football offices at Stanford and Washington also tweeted condolences.

“Needless to say, the Cal family is heartbroken,” athletic director Sandy Barbour said, fighting back tears. “There is no greater tragedy than for us to lose one of our incredibly bright and passionate young people far too soon.”

Batten said the training run was supervised by Cal athletic department medical staff, something he said always is the case. Campus spokesman Dan Mogulof added that Friday’s run was no different from those Agu had participated in “dozens of times.”

Agu played in seven games as a backup last season, recording six tackles.

Dykes said Agu was enthusiastic in everything he did, including his workouts.

“He attacked that with the same vigor he did preparing to play in the game,” Dykes said. “He loved to learn, loved to laugh.”