Earlier this offseason, former Colts wide receiver Austin Collie announced his retirement from playing pro football, as he will instead work at a concussion research clinic in Utah.
It was a series of concussions that derailed his NFL career, and today he wrote a piece for Bleacher Report about his career with the Colts and those concussions. It's a tremendous read that is well worth your time.
Collie writes about his serious concussion in 2010 in Philadelphia in which he was knocked out for several minutes (a very frightening moment I'm sure many Colts fans remember), as well as the ensuing concussions that he later suffered.