Junior Seau
Credit: Al Pereira / Getty Images

Why he hung it up: The NFL is a tough place for a 36-year-old linebacker.

Why he returned: Seau was tougher. He spent four days retired, then signed up with the New England Patriots in August, 2006.

His Success:
He was a team captain and played in all 16 games during the Patriots undefeated regular season in 2007. Unfortunately the extra hits may have exacerbated the brain trauma the led to his suicide in 2012.