By Adam Dettelbach
The Study
I collected data on 80 NFL running backs from the last two seasons who had at least six starts or 150 carries, as well as the run blocking data from all five of their offensive line slots and tight ends, using Pro Football Focus’ run blocking grades and Pro Football Reference’s rushing statistics. The goal was to determine which position is most important for an RB’s YPC (Yards-per-carry) statistic.
As control variables (and potentially as measurements of other possible significant causes of rushing success), I also measured the weight, age, 40 time, and QB NYPA (net yards per attempt) statistics to account for different possible causes of high YPC stats. Along the way, I took the average and minimum (lowest among the six blocking positions) value of each RB’s O-line’s run blocking grade to see if either figure would correlate with high YPC figures.
The Findings on Offensive Lineman Positions and Other Control Variables
When I put the six blocking spots, along with QB NYPA, weight, age, and 40 time all into a linear regression with the RB’s YPC as a dependent variable, I found that only two variables were statistically significant: Left Tackle grade and Tight End grade. LT had a p value of .089, with a coefficient of .007, meaning that for every 1-point increase in LT run blocking grade (on a scale of 1 to 100), that LT’s RB’s YPC can be expected to increase by 0.007. Meanwhile, TE had a p value of .074 and a coefficient of .013, meaning that for every 1-point increase in TE run blocking grade, that TE’s RB’s YPC can be expected to increase by 0.013.
LT is generally thought to be the most important offensive line position along with Center, so the importance of the LT slot is not unexpected, but the high TE importance is likely due to the fact that a bad TE is far worse at run blocking than a bad offensive lineman, and therefore can bring down a running play more easily than any other slot.
The next most significant variables were age (p = .18) and Right Guard grade (p = .28), neither of which was significant, but both of which were notable enough to possible become significant with a larger sample size.
All other variables had p values over 0.4, although each had a coefficient sign (+/-) that corresponded with its expected value except for LG.
The Findings on Average on Minimum
The figures for average run blocking grade and minimum run block grade completely flipped vs my expectations, and provided easily the most interesting results of the study. While average run block grade had a respectable 36.7% correlation with a RB’s YPC, minimum run block grade had a far more significant 47.2% correlation, demonstrating that an offensive line is only as strong as its weakest link. For comparison, the correlation between the most important blocking position (tight end) and YPC was just 29.7%.
To further compare the importance of average and minimum run block grades, I ran a linear regression using those two as independent variables and YPC as the dependent variable, and once minimum run block grade was controlled for, the effect of average run block grade on YPC disappeared, with its coefficient registering at a measly 0.002 and p value of 0.83, compared to a coefficient of 0.030 and p value of 0.004 for minimum run block grade.
Finally, I ran a regression using minimum run block grade and the various control variables (weight, age, etc.) to further determine the effect of minimum run block grade on RB performance. The result was extremely significant: None of the control variables had p values below 0.3, while minimum run block grade still had a coefficient of 0.03, but this time with a p value of 0.0002, demonstrating extremely statistically significant results.
For visualization purposes, here is a comparison of average and minimum run block grade against YPC, with YPC on the Y axis and the run block statistics on the X axes:
What It All Means
The two big conclusions of this project are that tight ends and left tackles have the largest statistical effect on their RBs, and that a RB’s YPC is largely dependent on how good his worst offensive lineman is.
So when picking a RB in fantasy football, keep an eye out for two things. The first thing to look for is how well his LT and TE’s run block for him. The second thing to look for is how bad his worst blocker is, and whether that’s bad enough to bring down his performance, because as it turns out, an offensive line really is only as good as its weakest link.