RB Carousel Analysis

Introduction

During the Indiana game, several people (myself included) were irritated about the constant running back changes. Watching live, it felt like the backs would be pulled right after a solid run, and it seemed like the changes were hindering any back from establishing a rhythm. The RB carousel approach started last year, and while there were mixed feelings about it then, the grumbling has increased this year as the offense has turned into a train wreck. So, I decided to look back and see if there actually is any effect of the constant RB changing on rushing success.

-------------------------

tl;dr

- Michigan changes their running backs a lot (48% of the time)

- Michigan changes their running backs a lot even after successful runs (45% of the time)

- Following both unsuccessful AND successful runs, Michigan gains more yards on average when there IS a running back substitution

- But, Isaac and Higdon do tend to have higher rates of successful runs when they are given more consecutive carries

- Overall, Michigan tends to have a higher frequency of explosive runs on a back's first carry, but potentially at the cost of lower odds of sustained running success

- IMO, there is no evidence from this review to suggest that the RB carousel does more damage than good

-------------------------

Some notes on the methodology

- I looked at running plays with regards to yards gained and play success (at least 40% of first down yards, 70% of yards to gain on second, 100% of the yards on 3^rd and 4^th down)

- I only looked at running plays, so this does not track substitutions that occurred when going from a running play to a passing one, nor does it account for yardage or success/lack thereof on RB receptions

- I also did not consider a running play from Hammering Panda FB dives or WR runs as an RB change, nor did I include any garbage-time drives [not charted on UFR]

- This only looks at RBs substitutions, yardage, and success. It does not account for play type, blocking, or game context. However, neither do the criticisms of the RB carousel

-------------------------

Summary

Discussion

Michigan substituted their running back on 48% of running plays. I don’t have this number for any other team, but that is definitely a staggeringly high rate. And there certainly is plenty of fodder for potential questioning, as the running back got pulled after a successful run 45% of the time. Given the high substitution rate, the number of times the substitution happened due to fatigue is negligibly few (i.e. the Isaac long run than where he just stepped out of bounds), so this was almost always a strategic decision.

As would be expected, and probably on any team, there is a higher rate of substitutions after an unsuccessful running play than successful one. But I wouldn't be surprised if the difference in rate of substitution is much smaller for Michigan than most other teams.

-------------------------

Substitution Effects

So, we’ve established that Michigan changes RBs a lot (which we already knew), and that they often do it even if the previous run was successful (which confirms half of what we already thought). Now, we need to see whether or not these substitutions actually affect the success of the following play:

Discussion

This chart categorizes runs as either successful or unsuccessful, and then looks at the next play and whether or not there was a running back substitution, and then finally the average yardage of the next run and the rate the next run was successful.

As one would expect of the coaches, following an unsuccessful run, there is a higher average yardage gained after a substitution compared to keeping in the same back. However, there is a decrease in the success rate of the following play when there is a substitution (more on that to follow).

Now, the key metric for us armchair coaches is in the comparison of the latter two classifications. If our ire is well-placed, we should see that substitutions lead to fewer average yards gained and lower success rates on the following run. However, we instead see a much higher average following a substitution, and there is no difference in the success rate following substitutions compared to keeping in the previously successful back.

-------------------------

Consecutive Carry Breakdown

With that stunning defeat in mind, we must consider that the previous chart is a limited overview. What about the possibility that the constant substitutions hinder Michigan backs from sustaining momentum?

This is a more difficult question to answer, but one possible insight is to compare the average yardages gained and success rates as running backs are given more consecutive carries prior to substitution.

Here is the overall breakdown:

Discussion

(2 MGoPoints to the first poster to correctly guess which back was given 8 consecutive carries, and 2 more for the game.)

This shows that explosive runs come most often on running backs’ first carries. However, the success rate does tend to increase as backs are given more consecutive carries. (The highest consecutive carries have the major caveat that they came in end-of-game, obvious running situations.) This suggests that the RB carousel strategy seems to create more explosive runs, but it may be at the cost of decreased success rate.

-------------------------

Breakdown by RB

Finally, I wanted to break this down further by each running back. Since Isaac and Higdon are more traditional, workhouse backs than Evans, who is a more change-of-pace back, it would seem like they would be more susceptible to having their momentum limited by the frequent substitutions. (I took some liberties in deciding how many consecutive carries to graph, based on sample size and whether or not the highest consecutive carries came in end-of-game situations as mentioned above).

Discussion

Not surprisingly, Evans saw a decrease in yardage productivity as his carries increased, and no effect on success rate. This goes along with the idea that he is more of a change-of-pace runner.

Both Isaac and Higdon are very productive on their first carries, but they do tend to produce more successful runs on average when they are given more consecutive carries. While the data on higher consecutive carries is limited by sample size, the trend of increasing success rate on additional consecutive carries does follow with the idea of those two as more workhorse backs.

-------------------------

Summary

Overall, as stated above, this review suggests that the RB carousel may possibly decrease Michigan’s potential success rate on rushing downs, but it is correlated with more explosive runs and no sacrifice in average yardage gained. There is also no evidence that substituting after a successful run makes Michigan any worse off. It will be interesting to see if the frequency of RB substitutions decreases after Higdon produced the first 200-yard game in a decade. But, if not, I will try my best to keep the grumbling down if I see him get pulled after a big run or two.