The SoapBoxers

How long can Trent Richardson expect to play in the NFL?

The topic comes up every year: how long is the average football player’s career?  People are particularly interested in the length of an NFL running back’s career, since it seems that injuries often cut their careers short.  This is often given as 4-5 years, with some estimates coming in as low as 2.5 years.

As is often the case, methodology is going to be very important.

Perhaps the worst methodology I have ever seen was looking at the current starting running backs and calculating the mean number of years they have been in the NFL.  However, this uses mid-career numbers and is going to underestimate the reality.  Would you take a 2 year old, 45 year old, and 75 year old and simply use the mean of their ages (40.67) and declare this to be the average life span?  Of course not – nor should you use mid-career numbers to calculate the average length of career.

The second issue is the decision of whom to include.  Do we include ALL NFL running backs, even the guy from Kosmo State who went in the 7th round and narrowly held onto a roster spot for a year before getting cut?  This guy’s career was cut short by lack of talent, not by injury.  We need to separate the wheat from the chaff and determine the average career length of a GOOD NFL running back.  I doubt that the casual fan is too concerned about how long her team’s third string back will kick around the league.

My methodology

There are two decisions to be made with the data.  The first is how to quantify “good”.  I’m going to take the years 1991-2010 and look at running backs who finished in the top 20 in the league in rushing yards at least once during that twenty year span.  My thought is that if you’re a good running back – the type that carries a team – you’re going to land in the top 20 at some point.  Maybe not every year, but at least once.  This is going to miss some situations like guys who are part of a tandem backfield for their entire career, but it should at least provide a decent sample size to work with.  I am excluding active players (defined as players who played in 2011), because of the problem with mid-career numbers.  Rushing yards isn’t a perfect barometer, but it should be fairly sound.

The second decision is what is meant by “length of career”.  Years can be messy – if a guy plays 9 games, does he get credit for a year?  I decided to just scrap the idea of years and go with games instead.

The data

Twenty years of top 20 lists means 400 names.  However, many players made the list multiple times.  There were 150 unique names on the list.  40 of these players are active, leaving 110 retired players in this group.  Here is the list, in order of most to fewest games played.

 
Mean: 109.4

Median: 103.5

If we divide these numbers by a 16 game schedule, we get 6.8 years for the mean and 6.5 for the median.  However, it’s important to note that it’s pretty common for a player – in any sport – to get dinged up and miss a game every one in a while.  So even a generally healthy running back would generally stretch these games out over 7.5 – 8 years.  Only 27 of the 110 players in the group had a career of 80 games or fewer (5 full seasons).

Most likely, a running back with Trent Richardson’s pedigree can bank on an eight year NFL career.  Longer if he’s lucky, shorter if he’s not.