2. Mel Farr
The Detroit Lions thought that they had themselves a future Hall of Famer in Farr, but that turned out not to be the case. The running back had an outrageous rookie season but suffered one of the worst sophomore slumps on this list. The trouble was that this turned into a neverending career slump thanks to injuries.
Farr rushed for over 1,200 yards in 13 games, as the Lions’ offense compiled over 2,000 yards between them. But it took six seasons for him to add another 1,200 to his career total. He fell to under 600 yards in his second season with just three touchdowns, compared to six the previous year.