So I was curious about the small running back success rate and did a search of every season by RBs 205 pounds or less over the last five seasons and sorted by PPR fantasy points. I chose PPR because presumably this is the format small backs are most likely to have success and I chose fantasy points because that's what we really care about and this way receiving and rushing points are included altogether.
I found 206 discrete seasons by RBs 205 or less in the past five years.
Out of 206 seasons, 25 seasons produced 160 fantasy points or more. Among these successful seasons, seven RBs had more than one season above 160 fantasy points in the past five seasons:
McCaffrey 3, Ekeler 2, James White 3, Tarik Cohen 2, Philip Lindsay 2, Theo Riddick 2, Dion Lewis 2. I would suggest that if there is a secret sauce to success for small backs in the modern NFL we should look at these backs and look for commonalities in terms of skills and situations. Not sure what that might be and don't have time to delve into this farther atm.
Overall, 25 successful season out of 206 seasons is not a high success rate but how does it compare to RBs 206 and heavier?
http://pfref.com/tiny/gTfIM
So it turns out there are many more successful seasons for players 206 and heavier: 103. But there are many more seasons played by such players: 607. Obviously there are more RBs above 206 so the dataset is larger.
But the success rate is higher for larger backs: 17% vs 12%.
http://pfref.com/tiny/OE9mm
Conclusion:
There is a statistical correlation between backs above 206 and fantasy success, even in PPR.
There are a select few small backs who do find success and the ones that have can do so for more than one season--ie., they can provide consistent fantasy production.
All things equal, drafting a back above 206 is more likely to succeed but don't ignore the small guys as a rule.
I would like to hear more about what separates the small backs who have found consistent and recent success.