Bret Bielema apologized Friday for an insensitive remark related to the death of California football player Ted Agu and after Cal athletic director Sandy Barbour criticized the Arkansas coach.

Bielema had used Agu's death as an example of college football's need to slow down offenses with a proposed rule change that would allow for defensive substitutions.

Responding this week to claims that there is no evidence to support fast-paced games leading to heightened injury risks, Bielema said the proof is in "death certificates. There's no more anything I need than that."

The 21-year-old Agu died of yet-to-be-determined causes on Feb. 7 after a training run with Cal teammates.

After returning from a memorial service for Agu in his hometown of Bakersfield, Calif., Barbour said Friday on Twitter, "Bret Bielema's comments about our Ted Agu are misinformed, ill-advised and beyond insensitive. Using the tragic loss of one of our student-athletes as a platform to further a personal agenda in a public setting is beyond inappropriate."

Bielema responded by issuing an apology.

"It was brought to my attention that remarks I made yesterday evening while discussing a proposed rule change were unintentionally hurtful. I am very passionate, as we all are, about the serious nature of protecting the well-being of student-athletes," Bielema said. " ... In my press conference last night, I referenced information about the tragic loss of a life of a student-athlete. My comments were intended to bring awareness to player safety and instead they have caused unintended hurt.

"As a head coach who works with young individuals every day, the passing of Ted Agu is a reminder to us all how short and precious life is. I would like to extend my deepest condolences and sympathy to the Agu family, coach Sonny Dykes and to the University of California family."

Bielema referenced Agu in his argument for approval of a proposal that would make offenses wait at least 10 seconds once the 40-second play clock begins to snap the ball. Bielema and Alabama coach Nick Saban are proponents of the change, which they say would allow defenses enough time to substitute players and help avoid injuries.

"I'm talking about the concussion crisis, sickle cell trait," Bielema told Sports Illustrated. "This one (sickle cell trait) really scares you because you don't know when it's coming. The kids have difficulty breathing. They don't want to come out of practice or the game.

"All the ones I've ever been around, they want to stay in because they don't want their teammates to think they're quitting or stopping. What we began to rationalize is that when these players pass when they're involved in these conditioning drills, they pull themselves out of it or the trainer pulls them out of it because they're having difficulties.

"What if you're in the middle of the third or fourth quarter and you know that the kid standing 15 yards away from you or on the other side of the field has this trait. He's got this built-in possibility of something happening. Your doctors have told you about it. Your trainers have told you about it. He looks at you through those eyes or maybe the trainer even says, 'Hey coach, you need to get him out of there.' And you can't. You have no timeouts. He's not going to fake an injury. He's not going to fall down."