3. Ki-Jana Carter — Retired at 31 years old in 2004
Kenneth Leonard “Ki-Jana” Carter was the #1 overall pick in the 1995 NFL Draft, after running for over 2,500 combined yards and scoring 35 combined touchdowns during his sophomore and junior seasons at Penn State. An All-American in 1994, Carter was a huge part of the Nittany Lions team that won the Rose Bowl that year, and was one of the first players that legendary head coach Joe Paterno actually encouraged to forego his senior season in college.
But after being taken by the Cincinnati Bengals, Carter tore ligaments in his knee on his third carry of the preseason, and missed his entire rookie year. In 1997, 1998, and 1999, he suffered season-ending injuries to three different parts of his body.