He actually came back fairly well in 1969 after his first knee injury, but when he was injured again in 1970 he wasn't able to come back at any level of effectiveness (he played in two games each in 1970 and 1971, with less than 100 yards total and less than 3 yards per carry each year). It would have been nice to see what he could have been if only he played 10 or 20 years or so later, with substantial improvements in knee surgery. Randy Hundley is another player who was never the same after injuries. How about Terrell Davis? MVP, Super Bowl MVP, 2000 yard season...ACL tear...never came close agina, retired 3 years later.