Another Look at the Penn State RB Position: Success Rate, Yards Gained Distribution, and Standard Deviation

With Noah Cain out the last two weeks, we’ve seen a lot more of Journey Brown in the run game as the official RB1 — he’s handled nearly 50% of the workload in the past two games. It’s been exciting at times, given Brown’s big-play ability in both the run and the pass game. However, he’s always felt like a boom-or-bust back to me. I wanted to see what the data showed and see if my impression was true.

While Brown has been leading the RB committee most of the season in yards per attempt both on the ground and in the air, the fan consensus has been for Noah Cain to be RB1. I have been wondering why this has been the case, given that both Brown and Devyn Ford have better YPA than him. The only conclusion I could draw, given the eye-test and feedback from loyal PSU fans, is that Cain is the more “reliable” back. Some people call this “success rate”: the percentage of plays that are deemed “successful”.

In essence, this looks like:

  • gaining 5 yards on 1st and 10
  • 70% of the yardage to go on 2nd down
  • all the remaining yards to go on 3rd or 4th down.

Success rate is factored into PPA (Predicted Points Added), the cousin of EPA. At a glance, justifying the majority opinion is the fact that Noah Cain leads the RB committee in PPA (Data is courtesy of CollegeFootballData.com, and you can see this data for yourself here).

Noah Cain leads all PSU RBs with .261 average predicted points added in the 2019 season.

I decided to look at it in two additional ways: the distribution of yards gained on each run, and the standard deviation of run plays. Let’s take a look at the graph first.

Distribution of yards gained on run-plays only, for the Penn State rushers.

This graph shows us how many yards each runner gains, bucketed into groups of 5 yards. I limited the graph to 20 yards so we can compare everyone easily, but this doesn’t do Brown justice in terms of just how explosive he can be. Even from this graph, we can see that he has a higher percentage of rushes of 10+ yards than any of the other feature backs. What the graph doesn’t show is that he also has five runs of greater than 20 yards, the most of any RB. Noah Cain has the fewest.

With all that being said, we can quickly see that Noah Cain (top right) is the most consistent in short-yardage situations, which is why so many fans love him. Quite simply, he gets first downs. Cain has the largest proportion of his runs that go for 5-10 yards. He doesn’t get many gains of larger than that, but he also doesn’t lose yards too often. While more explosive, both Brown, Ford, and Slade have a considerably larger portion of their runs going for less than 5 yards.

Finally, let’s look at the standard deviations of these backs’ yards per play. This will give us an idea of how much variation there is in their yards per attempt. For a simple example, if a running back ran for 5 yards every time, his mean would be 5 and standard deviation would be 0. If a running back averaged 5 yards per attempt, but only ran for either 10 yards or 0, his standard deviation would be 5, indicating more of a boom-or-bust style back (this is a rough estimate).

Average yards per attempt (mean) and standard deviation of rushing attempts for Penn State rushers.

So from this very exciting chart, a smaller standard deviation implies a more consistent back with less variation in each individual run play. Cain’s is considerably lower, at 4.7 yards, than the rest of the top backs. Ford and Brown, unsurprisingly, lead the way in terms of variability in their run plays. This chart further validates what the histogram above was hinting at.

While Brown (and Ford) are certainly the undisputed backs with big-play ability, when you need a first down and a reliable few yards, Noah Cain still appears to be the guy. His status for Saturday is still up in the air, but Lord knows we’re going to need plenty of both to have a shot at the upset against #2 Ohio State.

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