Analyzing RB Hierarchies & Career Spans (Fantasy Football)

As the league shifts towards a multi-RB backfield, it is crucial to understand RB hierarchies and how having a shared backfield impacts fantasy performance. In this article, we will explore this question and look at some RBs who might be nearing the end of their fantasy-impact careers.

Editor’s Note: For more on the performance of RBs factoring in age, check out the Lifecycle of a Dynasty RB by Marvin Elequin.

RB Rush Shares

The first thing we will look at is rush share (the percentage of carries a running back receives on their given team) on a team-by-team basis. In the following graphic, you can see the progression of each team’s RBs and their rush share (RBs with one-year tenures are not shown) as well as their fantasy points per game (half PPR scoring). It should immediately become apparent that only one RB can command the fantasy output at once.

Typically, we only see strong fantasy performances from backs with over 35-40% rush share–it is incredibly difficult to generate points with less volume. We see this in the case of BAL, DEN, DET, HOU, KC, and NE, where their split backfields never allow for a true RB1 candidate averaging over ~12 points per game to emerge.

With that in mind, let’s take a look at some RBs that you might want to avoid because of their low rush shares.

As all of these players are featured in split backfields and they have never had the opportunity to act as a bell cow back putting up RB1 numbers. Unfortunately, most of them will never get that chance. While there is a lot of hype surrounding players like Herbert and Cook, it is smart to be wary of them come draft day, as they can easily be overvalued.

RB Lifespans

Earlier, you might have noticed the short lifespan of RBs with high rush shares, but low PPG–let’s dig into this. Multiplying rush share by fantasy points per game gives us a good idea of how running backs are playing relative to their volume. We will call this new stat ‘Rush Share times Individual Points for’, or RSIP. After running the numbers, I found that RSIP doesn’t have an effect on RBs’ career spans–the plotted distribution of these two was very random.  It does, however, impact their years remaining as a starter. In the plot below, it is apparent that especially as backs get older, the worse their RSIP is, the less time they have holding the reigns of the backfield.

Since we are looking at a fairly linear relationship, I built a simple linear regression model to give us an idea of how many years RBs may have remaining, according to their RSIPs. Let’s take a look at some rushers who might be on their way out.

Let’s break this down further:

• While Nick Chubb still has a good amount of time on top, if he continues to play as he did in the back half of last season, his starting job could be in jeopardy in a year or so.
• Joe Mixon and Najee Harris both have high rush shares but have young RBs on their tails. If they continue to underperform, the two-year prediction will come true.
• Miles Sanders and Aaron Jones are both aging backs with low RSIPs. This two-year window seems accurate, especially as their backfields become more split.
• Surprised to see Pierce and Etienne on this list? Both backs saw high rush shares in 2022 but posted low RSIPs, relatively. If their underperformance continues, they will be out of a starting spot within two years.
• David Montgomery has put up a very low RSIP despite a high rush share–with Jahmyr Gibbs arriving in the Detroit backfield, Montgomery likely only has 1 more season left as a starter.

That’s all for this article! If you have any questions, feel free to reach out on Twitter!