The undrafted linebacker will never play football again after he suffered an on-field stroke in Jacksonville's loss the Buffalo Bills last December.
Doctors have discovered that a dime-sized portion of Allen's cerebellum -- part of the brain that tells the body how to run and walk -- has gone dark.
"It was strange because it was so routine," Allen said. "We hit, I got off the block, no big deal. I felt something flash -- like they say when you get your bell rung. I didn't lose consciousness. I walked back to the huddle and finished the drive."
Allen stayed on the field, battling double vision until the final whistle. The Jaguars, later that week, shut him down after medical tests revealed the truth, marking the end of a promising young career that saw Allen start 29 games over the past two seasons.
With a young wife and a 2-year-old son at home, Allen understands that walking away from the game is wise, saying: "For generations football has been tough guys, and that's how it has to be. But there's a fine line."
We send our best wishes to Allen and his family and encourage you to read the rest of his story here.