By Max Mulitz
Background Research: Brian Burke, who heads the football analytics department for ESPN (the worldwide leader in sports) showed Runningback Success Rate is more strongly correlated with winning than Yards per Carry. However, it is unclear how much the down and distance situations where teams choose to run effects success rate, compared to the actual talent of the players.ArmchairAnalysis defines success in the following manner: “Generally, a play is deemed ‘Successful’ when the following occurs: 40% of yards-to-go are gained on 1st down; 60% of yards-to-go on 2nd down; or 100% of yards-to-go on 3rd & 4th down.”
Using data from Armchair Analysis from the 2011 through 2015 seasons, I was able to construct the following chart showing expected rushing success rate by down and distance.
We can see that rushing success rate clearly decreases as yards to go increases and that rushing success rate is generally lower on 3rd down than on the other downs.
By looking at the differential between a players success rate and the success rate that would be expected based on the down and distance situations where they got their carries, we can look at a running backs success rate independent of how they re being used.
The percentage of a players carries that are successful is the players Success Rate. The average success rate for rushes over all the situations where a player gets the ball is the players Expected Success Rate. We will futherdefine the difference between a players actual success rate and their expected success rate as their Success Rate Differential, which is success rate compared to average.
Findings: The Year to Year Correlation for Success Rate for Runningbacks with consecutive 100 carry seasons between 2011 and 2015 (Sample Size=106) was .26 and the correlation for Success rate differential was only .20, however the Year to Year Correlation for Expected Success Rate was .43, meaning a runningbacks’ success rate as a function of their role is more stable year to year than the success rate experienced as a function of their talent (as measured by differential from expected success rate.)
It is also worth noting that Expected Success Rate ranged from 41% to 51% in the sample, a significant distribution, so if you compare running backs based only on success rate you are capturing a lot of situational effects.
While differential only weakly predicts itself, previously years differential is significant at P=.05 when trying to predict current years differential. The coefficient for previous years differential is .21, so a RB who performs 5% above average would be expected to regress to just over 1% above average the following year.
Case Study: Mark Ingram of the New Orleans Saints was a 1st Round pick (28th Overall in 2011)
*Ingram did not receive 100 Carries in 2013 due to injury
The average success rate for a 100+ carry RB was 45.5%, so Ingram was above average in 3 of the 4 years. However, once you adjust for the expected success rate based on the situations in which Ingram got the ball, we see his success rate is approximately average to slightly below average over the four year sample. Success rate overrates how successful the Saints have been when rushing with Mark Ingram.
Case Study 2: The New England Patriots have had a 100+ Carry back with a 49%+ Expected Success Rate each year. 3 different players have served this lead back role over the timespan.
*In 2014 only 60 of Blounts 125 Carries came with the Patriots, early in the season he played for the Steelers
It is unclear if the relationship between Saints and Patriots high Win % in the sample (56% and 76%, respectively) and their above average rushing success rate is driven more by runningback talent or choosing to run in high success rate situations.
Conclusions: After adjusting for situation, a runningbacks previous years Success Rate is a weak but still statistically significant predictor of the next years Success Rate. Only about 20% of the difference between how successful a running back is compared to expectation persists from year to year.
These findings disprove the idea that rushing success rate is a pure or approximately pure measure of running back talent. These findings also strongly suggest that at least part of the relationship between rushing success rate and winning is caused by teams choosing to run in advantageous situations and not just teams having more rushing talent than others.