NFL medical officer defends how Colts handled Jacoby Brisssett

— -- The NFL's chief medical officer is defending the Indianapolis Colts' treatment of quarterback Jacoby Brissett, who was allowed to return to Sunday's game against the Pittsburgh Steelers after a hit to the back of his head. Brissett was placed into the NFL's concussion protocol when he reported symptoms after the game.

"All of our protocols were followed," Dr. Allen Sills said Tuesday on a league conference call. Sills added that Brissett "had no symptoms" and that there were "no findings" during the game to prevent him from returning to play.

Sills confirmed that Brissett passed three separate concussion tests, two during the game and one immediately afterward. He said it is not unusual for concussion symptoms to evolve and emerge in a delayed fashion.

Brissett reported the onset of what Sills said were "mild" symptoms about 20 or 30 minutes after the game.

"Out of an abundance of caution," he was placed in the protocol, Sills said.

Sills said concussions are "a very heterogeneous injury" in that symptoms vary widely. For example, some people have many symptoms right away, whereas others start with one symptom and then have others later.?

"It's part of the frustration of us as medical practitioners trying to care for [concussions]," Sills said. "We recognize that concussion is not one injury. It's a spectrum of injuries that are going to have a lot of different presentations. And it is still part of what we, as a medical profession, must better understand this injury so that we can better categorize it and continue our efforts to diagnose it."

Sills said he could not comment on whether the Seattle Seahawks followed protocol in allowing quarterback Russell Wilson to return to a game after being sent off the field for a test? Thursday. The NFL's investigation into that episode is ongoing.