18. Gale Sayers – Retired at 28 in 1972

In his first three seasons in the NFL, “The Kansas Comet” put up a staggering 6,401 yards total yards from scrimmage (rushing, receiving, and returning punts and kicks) winning the rookie of the year award in 1965 and being named to the Pro Bowl in each of those three seasons.

However, midway through his fourth season (in 1969), Sayers tore the ACL in his right knee. While such an injury has become common in today’s NFL, and the recovery has become even more routine, orthopedic surgeons at the time lacked the sophistication and technology that we enjoy today.

Even though he was still named to Pro Bowls and All Pro teams when he returned to the NFL in 1969, Sayers was never quite the same player after that injury. Sadly, Sayers actually ended up injuring his other knee in 1970, and was never able to rehabilitate it to the point where he could resume his NFL career. He played in only two more games after that (in 1971), and ended his career having played in a grand total of 68 games (less than four-and-a-half seasons).