2022 49ers Backfield Breakdown: Shanahanigans

by Noah Hills · Analytics & Advanced Metrics

The 2022 49ers Backfield Breakdown is part of an offseason series in which I take a deep dive into one NFL team’s backfield and examine the respective rushing performances of the players in it. In doing so, I hope to gain insights into key players from a talent evaluation standpoint, and using that evaluation as a baseline, from a dynasty valuation standpoint. The first installments in the series can be found here.

I’ll start by taking a quick overview of each team’s raw rushing volume and propensity to run the ball in general, and then dive into the player evaluation portion. Before we start, let’s define the metrics I’ll use as part of those evaluations:

Key Metrics

Yards per Carry+ (or YPC+)

The degree to which a player’s raw yard per carry average exceeds or falls short of the collective yard per carry average of all other running backs on his team. Meant to be an overview of a player’s team-relative efficiency.

Box Count+

The degree to which the average amount of defenders in the box that a player faces on his runs exceeds or falls short of the collective average faced by the other running backs on his team. Considering that the outcome of any given rushing attempt is largely dependent on the amount of defenders in the box pre-snap, Box Count+ describes the relative degree of difficulty of a running back’s carries.

Breakaway Conversion Rate (BCR)

Quantifies performance in the open field by measuring how often a player turns his chunk runs of at least 10 yards into breakaway gains of at least 20 yards.

Box-Adjusted Efficiency Rating (BAE Rating)

Improves upon YPC+ by accounting for the box counts that a player carried the ball against. Looks at team-relative yards per carry against each individual box count, then uses a weighted average (based on total carries against each box count) to generate an overall score. A score of 100-percent indicates that a player is producing exactly the per carry output of his teammates, a score above 100-percent indicates that he is outdoing their per carry output to whatever degree, and vice versa for a score below 100-percent.

Relative Success Rate (RSR)

Measures player consistency using Success Rate, but relative to his teammates and adjusted for the box counts that he faced in the same way that BAE Rating is. “Success” on a given carry is defined by gaining 40-percent of yards needed on first down, 70-percent of yards needed on second down, and 100-percent of yards needed on third or fourth down. A score of 0.0-percent indicates that a player is succeeding on exactly the same percentage of his carries as are the other backs on his team, a positive score indicates that he is succeeding more often than his teammates are, and vice versa for a negative score.

Volatility Rating

Measures the disparity between a running back’s percentile ranks in BAE Rating and RSR in order to indicate how volatile a player’s per-carry performance is. High overall efficiency paired with low rate of success indicates boom/bust output, while low overall efficiency paired with high rate of success indicates steady, low-ceiling output. Measures degree of volatility, not quality of performance.

Composite Efficiency Score (CES)

Presents a single-metric overview of the quality of team-relative performance a player produced on his carries in a single season. Calculated using the average of a player’s percentile ranks in Box-Adjusted Efficiency Rating and Relative Success Rate, represents player performance on a 0-100 scale.

Team Rushing Volume

The San Francisco 49ers finished No. 6 in the league in total rushing attempts last season. Their 499 carries were almost 50 more than the NFL average. Last year marks the fourth time in five seasons of the Kyle Shanahan era that they were in the top half of the league in rushing volume; and the second time in the last three years that they finished in the top six.

The 49ers are not just run-heavy from a raw volume standpoint. According to rbsdm.com, they ranked No. 3 in the NFL in early-down run rate in neutral Game Script situations (when win probability for either team did not exceed 80-percent) last season. And they ranked No. 6 in the same category from 2017-2020.

The 49ers were also very run-heavy relative to expectation (given league-wide play-by-play data) in nearly every down-and-distance situation in 2021. They ran the ball 7-percent more often than expected overall; calling runs much more often than expected on 2nd-and-medium (+12-percent), 2nd-and-short (+11-percent), and especially 3rd-and-short (+31-percent!) situations.

Shanahan loves his running game. San Francisco has been a run-heavy team nearly every year of his tenure, regardless of personnel or in-game situation. We should expect that to continue going into 2022.

Efficiency Numbers

Fifth-round rookie Elijah Mitchell came out of almost nowhere to lead the 49ers in rushing last season. Behind him, there were seven guys who saw work on the ground in San Francisco. Here are the complete rushing efficiency profiles for each of those players:

Easily the most impressive ballcarrier for the team was Deebo Samuel. Among all runners with at least 10 carries last season, Samuel ranked second in Composite Efficiency behind only Najee Harris. He was one of only four players (along with Harris, Jonathan Taylor, and Duke Johnson) to have a CES above the 90.0 mark on at least 50 carries. He was generally running into Mickey Mouse defensive fronts. But he was both consistent and dynamic on the ground even considering the relative ease of those carries.

Mitchell had a productive season. But he didn’t offer much on a per-touch basis above and beyond what the team’s other runners produced. His Box-Adjusted Efficiency Rating falls in the 42nd-percentile, while his Relative Success Rate was a 40th-percentile mark.

More Context

Elijah Mitchell does look better if we remove Deebo Samuel‘s carries from the team sample. In that case, his BAE Rating and RSR numbers would jump up to the 67th and 54th-percentiles, respectively. It does make some sense to consider Mitchell’s team-relative performance outside the context of what Samuel did in this offense given that he is not technically a running back. But these metrics only look at production on traditional run plays. We’re only looking at what he was doing while lined up as a running back. So he’s not getting credit for production on jet sweeps and gadget plays. Mitchell was fine last year. But there were yards available in this offense that he failed to gain; evidenced by what Samuel was able to do on a per-carry basis.

Outside of those two guys, Jeff Wilson and Trey Sermon were equally ineffective in limited work. JaMycal Hasty succeeded on seven of his 16 carries. Raheem Mostert, Jacques Patrick, and Trenton Cannon were collectively good on a minuscule sample propped up by an 11-yard Mostert carry.

So Now What?

Raheem Mostert, Jacques Patrick, and Trenton Cannon are now gone. And it’s likely Deebo Samuel won’t play in the backfield nearly as much going forward. JaMycal Hasty and Jeff Wilson are still under contract. But the main players on this depth chart will be Elijah Mitchell, Trey Sermon, and third-round rookie Tyrion Davis-Price.

Mitchell should be the de facto starter, but I wouldn’t rule out Davis-Price for a substantial role. At 6-0 and 211-pounds with 4.48 wheels, he fits the traditional mold of a 49er running back as a thinly built, straight-line speed guy much more than Sermon does. Davis-Price was also solid as the lead back at LSU in 2020 and 2021. He posted positive BAE Ratings in both of those seasons to go along with the best career Relative Success Rate mark among any runner in the 2022 Draft class.

Mitchell is more reasonably priced now than he was earlier in the offseason. But he can still be flipped for mid-first round value in rookie drafts. Considering his prospect profile, the draft capital spent to acquire him, and recent history regarding the replaceability of San Francisco running backs, I’d be selling for those kinds of returns.

Davis-Price, on the other hand, is currently priced as if he has no shot at a legitimate role this season. He’s being selected in the mid-third round of rookie drafts and as the RB48 startups, well into pure handcuff range. He’s a value.

Final Word

The most productive running back for the 2023 49ers could very easily not be on the roster right now. And the most productive could very easily not be the most expensive one in the dynasty marketplace. His current cost is palatable, but I’m still divesting out of Elijah Mitchell and taking cheap shots on Tyrion Davis-Price. Trey Sermon might not be dead either. The main thing is that nobody knows what’s happening in this backfield year-to-year, so treading carefully is the move.