Assuming Chris Johnson plays this season, with or without a new contract, what can we reasonably expect from him, both this year and in the years to come?
To help answer that question, I gathered the stats of the NFL's leading rushers for the past 32 years to find out how they performed in the years following their league-leading seasons.
The collected data goes back to 1978, the year the league began a 16-game regular season. Nineteen players led the league in rushing for at least one year during that period. Five of them -- Earl Campbell, Eric Dickerson, Marcus Allen, Barry Sanders and Emmitt Smith -- are Hall of Famers and have combined for 17 of the 32 rushing titles. Four more -- Curtis Martin, LaDainian Tomlinson, Edgerrin James and Jamal Lewis -- have excellent credentials which will make them serious contenders for enshrinement when they become eligible.
That's a very elite group of players whose stats we're about to examine, along with those of the other stars who were good enough to lead the league.
The following chart lists the rushing yardage for each of the league leaders over the last 32 seasons. It then lists the yardage each back rushed for in each of his next five seasons.
As you can see, the players averaged 1,695 rushing yards to lead the league but averaged only 1,248 yards the following season, or 74% of the previous season's production. The productivity continued to decline in subsequent years, falling to 60%, 55%, 47% and 41%. The players barely managed to average 1,000 rushing yards only two years after leading the league.
History says Johnson should experience a similar decline. Applying these historical factors to CJ's 2009 season results in an expectation that he should rush for about 1,476 yards this year, or 73.6% of last season's production. He can also be expected to rush for around 3,777 yards in the three years remaining on his contract, an average of 1,259 yards per year.
According to the historical trends, CJ is not expected to gain over 1,000 yards in a season after his current contract expires in three years, so it would seem that CJ's expected shelf life as a top back approximates his contract. If the Titans want to throw a little more money at him in a new contract, that's fine. But as fans, we shouldn't expect more than a few more good years from him. History says it's unlikely to happen.