Running Back Growth Potential Starts with Size

Carolina Panthers RB Christian McCaffrey
Carolina Panthers RB Christian McCaffrey
Photo: USA Today Sports Images

He may never have been the consensus top choice in a fantasy draft, but Ezekiel Elliott is the perfect fantasy football player. His selection at fourth overall in the actual 2016 draft was a clear signal that he would start for the Cowboys immediately as a rookie. And since then, he has dominated the team's running back touches. He has never fallen short of 13 touches in a game and only five times fallen short of 18 touches. Since he has been healthy, Elliott has reached the rare benchmark of 300 PPR points in a season three times, tied for the most at his position in the last decade with Arian Foster and Le'Veon Bell. And Elliott would likely have gone four for four if he hadn't been suspended for six games to start his sophomore season.

I've been thinking about Elliott lately in relation to Christian McCaffrey, now the back with the best fantasy season of the last decade (470 points in 2019) and a player whose sophomore breakout in 2018 I did not see coming. It wasn't for lack of noise. In the preseason that year, beat reporters gushed that McCaffrey had put on muscle and was, as I read it, in the best shape of his life. That transformation was visible, but the latter cliché led me to underplay its importance. McCaffrey's 1.6 average yards after contact as a rookie was tied for fourth-lowest among the 47 backs with 100 or more carries in 2017. He had already been an important fantasy player, but more as a mislabeled slot receiver. I didn't expect the extra weight to turn him into Marshall Faulk.

McCaffrey enjoys his most obvious benefits from the extra weight on individual plays. He has increased his average yards after contact to 2.0 the last two seasons. But my reflection on Elliott and McCaffrey led me to conclude that weight has a greater importance for fantasy consideration in its impact on health. It is difficult to survive the workload needed to reach 300 fantasy points in a season. When you lay it out, the 20 backs who have reached that benchmark in the last decade look a lot alike.

Running Backs with 300+ PPR Points, 2010-2019
Player Height (In) Weight (Lb) BMI Seasons
Arian Foster 73 227 29.9 3
Le'Veon Bell 73 225 29.7 3
Ezekiel Elliott 72 225 30.5 3
Christian McCaffrey 71 205 28.6 2
Todd Gurley 73 227 29.9 2
Alvin Kamara 70 215 30.8 2
Matt Forte 74 218 28.0 2
LeSean McCoy 71 210 29.3 2
David Johnson 73 224 29.6 1
Saquon Barkley 71 223 31.1 1
Jamaal Charles 71 199 27.8 1
Ray Rice 68 212 32.2 1
DeMarco Murray 73 220 29.0 1
Adrian Peterson 73 220 29.0 1
Devonta Freeman 68 206 31.3 1
Aaron Jones 69 208 30.7 1
Doug Martin 69 223 32.9 1
Austin Ekeler 70 195 28.0 1
Marshawn Lynch 71 215 30.0 1
Maurice Jones-Drew 67 210 32.9 1

McCaffrey's listed weight for this exercise is his combine weight. That is the source of all of my height and weight measurements, and so it comes up short when players transform their bodies after they reach the NFL. But even taking that handicap, McCaffrey is one of just four backs who hit the 300-point benchmark with a body mass index (BMI) below 29.0. Several others, such as Devonta Freeman and Aaron Jones, have similarly low weights to McCaffrey, but their shorter heights suggest a compactness to their builds. Those vagaries make BMI a better way to predict players' abilities to survive heavy workloads. Just look at the trends of the running backs who reached 240 fantasy points in season. More than half of them landed between a 29.0 and 31.0 BMI.

Chart 1

As Fantasy Points' Scott Barrett asserted on the latest episode of the Football Outsiders Fantasy Podcast, bell-cow running backs move the needle of full-season fantasy success more than any other type of player. Fantasy players recognize that value in established bell-cow backs such as Elliott and McCaffrey who should again be top-five draft picks in most fantasy leagues this year. But they have a harder time with younger players who haven't yet provided clear evidence of their peak professional workloads. For me, the BMI trends make it clear that backs who fall in that 29.0 to 31.0 range are the best selections for possible breakouts.

Chart 2

A.J. Dillon (33.0) is the only young back on the high side of the BMI range who rings my alarm bells. And even if they haven't thought of it in these terms, the critics of the Packers' 2020 draft strategy are applying a similar logic. Dillon looks like the sort of specialized short-yardage back that modern teams have stopped drafting on Days 1 and 2. Derrick Henry may have provided a reason to question that wisdom as he carried the Titans to playoff victories over the Patriots and Ravens, but Henry is a freak, and the athleticism of his 6-foot-3 and 247-pound frame pops in his 30.9 BMI. At about the same weight, Dillon is 2 or 3 inches shorter. I'll believe he can carry the Packers rushing offense when he does it.

Boston Scott (32.8) and Clyde Edwards-Helaire (31.8) don't alarm me as much as fill me with questions. I suspect most readers would have expected the 5-foot-6 Scott to show up on the other end of the spectrum, but his 203-pound weight is actually quite a bit for his height. Darren Sproles and Tarik Cohen are the only other modern, relevant backs who are similarly short, and Scott has more than 10 pounds on each of them. Without a reasonable player to compare him to, Scott has a wide range of possible career outcomes.

It's no mystery why Edwards-Helaire is a first-round fantasy pick this season. He is a decorated pass-catcher. He is a first-round selection of maybe the most fantasy-friendly offense, the Kansas City Chiefs. And after incumbent starter Damien Williams opted out of the season, Edwards-Helaire is left with little apparent competition for touches this season. But I've noticed that Edwards-Helaire is often described as a bowling ball, which for me conjures memories of another 5-foot-7 back, Maurice Jones-Drew, whom I remember as a standout yards-after-contact player. Based on his scouting, Edwards-Helaire isn't that. He relies instead on his vision, his quickness, and his hands. NFL backs can certainly succeed with those defining traits, but Edwards-Helaire tested slow with a 4.60-second combine 40 time and didn't try the shuttle or 3-cone drills that could have confirmed his quickness. I won't advise you to avoid him in your first rounds, but you should consider following his selection with either Darrel Williams or Darwin Thompson as a handcuff in the late rounds, assuming their pecking order is clarified before your draft date.

The lighter side of BMI offers many more reasons to be cautious in your sleeper picks. The Ravens have made it clear in their touch allocations and drafting of J.K. Dobbins (30.7) that Justice Hill (27.3) is a specialized pass-catcher. But Elliott's seemingly obvious handcuff, Tony Pollard (27.8), is no sturdier in view of his 2-inch height advantage. I'm unsure he could replace all of his lead back's heavy workload if he had that opportunity for a month or more. And I feel the same about possible Titans and Raiders rookie handcuffs Darrynton Evans (27.9) and Lynn Bowden (27.3). Austin Ekeler (28.0) and Raheem Mostert (28.3) have already enjoyed fantasy success, but I think it's fair to question their abilities to further increase their career-high 2019 workloads. That may cap both players as RB2s, even in PPR formats.

Meanwhile, many of the most compelling examples of players whose BMIs run counter to their assumed ceilings play in Elliott's NFC East and its AFC equivalent. After Edwards-Helaire, the Eagles' Miles Sanders (30.0) and the Bills' Devin Singletary (29.5) are KUBIAK's favorite backs that have never run at the volume we project for them this season. I believe they have the size and the skills to handle featured roles, even if the latter team's selection of Zack Moss suggests otherwise. Washington's Antonio Gibson (28.4) has a receiving track record to make even Edwards-Helaire jealous, but his 221-pound weight plays down at his height of 6-foot-1 to 6-foot-2. A finally healthy Bryce Love (30.3) might sneakily be a better upside pick. And while Sony Michel's return to practice may refute expectations that he could miss the start of the season, Damien Harris (30.0) has the build of a player who could handle that workload. He is a worthwhile lottery ticket whatever Michel's status to start the season.

As I've presented things so far, size is more of a subjective consideration to apply to the backs you could consider as sleeper picks with a reasonable assumption that KUBIAK or any other projection system cannot perfectly predict which starters will get hurt or lose their jobs. That said, proximity to "ideal" size is a factor KUBIAK uses to project workload changes for players in the same backfield over the course of a season. Take the Washington backs for example. Love's size advantage carries a smaller but still present advantage in our overall growth expectation -- which also factors in recent historical usage, efficiency, and prospect status -- over Gibson. We project the former player for a 1.3-carry weekly shortfall to start the season. But with their different growth rates, Love gains 5.1 more projected carries over the course of the season and nearly catches up to the Gibson's projected weekly total by Week 17.

Projected RB Carries by Week, WAS, 2020
Wk Adrian
1 11.1 3.6 4.9 1.6
2 10.9 3.7 4.9 1.7
3 10.7 3.8 4.9 1.8
4 10.5 3.8 5.0 1.7
5 10.4 3.9 5.1 1.7
6 10.2 4.0 5.0 1.8
7 10.0 4.1 5.1 1.8
9 10.0 4.1 5.2 1.8
10 9.7 4.2 5.1 1.8
11 9.6 4.2 5.1 1.8
12 9.5 4.3 5.1 2.0
13 9.4 4.4 5.2 2.0
14 9.2 4.4 5.3 1.9
15 9.0 4.4 5.2 1.9
16 8.9 4.5 5.2 2.0
17 8.8 4.5 5.3 2.0
Projections unadjusted for venue, weather, or defense

We apply similar projected growths or declines to the backs and receivers on every team based on their potential and that of their teammates. And while that cannot simulate the repercussions the teams whose skill players suffer some major injuries this season will see, it does at least capture some of the value of player potential, even if that potential is unlikely to manifest as production at the start of the season.


8 comments, Last at 29 Aug 2020, 7:00pm

#1 by Lost Ti-Cats Fan // Aug 27, 2020 - 11:45am

Maybe I missed it, but shouldn't the % of backs scoring well be compared to the % of backs playing in the league at that BMI?  For example:

"Just look at the trends of the running backs who reached 240 fantasy points in season. More than half of them landed between a 29.0 and 31.0 BMI"

To determine whether that's a reflection of the value of having a BMI between 29.0 and 31.0, shouldn't we also have a reference to what % of the overall number of running backs fell within these metrics?  If 35% of all RBs sported a BMI of 29.0 to 31.0, that supports the idea that this is a sweet spot for top performers.  If 75% of all RBs had a BMI of 29.0 to 31.0, it suggests the opposite.

Points: 0

#2 by Scott Spratt // Aug 27, 2020 - 12:54pm

That was the approach that I wanted to take with the research, but I couldn't figure out a way for it to make sense.  There are a lot of lighter BMI running backs who play in the league but do so with a J.D. McKissic kind of workload.  He had 38 carries and 34 receptions last year.  I don't think anyone would consider him a real candidate to be a bell-cow running back.  The same is true for fullbacks who get used exclusively on third downs and the goal line.  Using the entire league as a basis of consideration in my mind makes the 29-31 BMI range look too important.  That's why I took my back-out approach to the research.  But I'd be interested to hear if you have other ideas of how to properly handle that.

Points: 0

#4 by Lost Ti-Cats Fan // Aug 27, 2020 - 8:05pm

Yeah, it's a big challenge, and no, sorry, I'm afraid I don't have any good solutions. 

As you say, intuitively I'd expect lighter RBs to more often be 3rd-down specialists and heavier RBs to be heavy-set specialists, but in the context of this purpose (fantasy point production) that may not pose a problem.  If being on either extreme limits the RB's usage, then I think that supports the proposition that there's a sweet spot where the RB's size tells you the RB has a better potential than a lighter/heavier player to generate fantasy points. 

But if we expect the RB to be used as a bell-cow, is his BMI relevant?  I'd surmise it may not be, or at least that this data doesn't provide much ammo one way or the other.  In which case BMI may primarily be useful as indicator of which young players may be selected for the bell-cow role, which is one of the key points of your article.  It just begs the question of how useful an indicator it is.

Maybe an analysis of BMI versus fantasy points, controlling for draft position, might suggest a trend for rookies and sophomores?  Sophomore data being less reliable due to the possibility of greater changes in BMI since the combine, as you noted re CMC.


Points: 0

#6 by Aaron Brooks G… // Aug 28, 2020 - 11:28am

It's pretty prone to outliers.

Chris Johnson ran for 2000 yards with a BMI of 27.2. Adrian Peterson just makes 29.

Points: 0

#3 by BiscuitsNGravy // Aug 27, 2020 - 2:09pm

Im not sure what you think you are capturing here; EXCEPT the preference for RBs that are 5'10"-6'1" and around 200 pounds amongst NFL team personnel decision makers.
You dont demonstrate that (BMI=29-30) backs outperform others, or that smaller backs underperform.

you observe that alot of the successful RBs are BMI29-30. 

are they BETTER than other backs, or just more numerous?


look at RB# rankings after season and see what BMI trend is.
look at YAcontact sorted by bmi

Points: 0

#5 by RobotBoy // Aug 28, 2020 - 5:14am

After an injury redshirt, or...something last season, I too expect that Harris will have some nice stats this season. Given that the Pats have about 12 decent RBs though, it's hard to see him amassing a lot of yardage. Belichick has really doubled down on the RBs and there might be a surprise cut or two coming.

Points: 0

#7 by Scott Spratt // Aug 28, 2020 - 2:27pm

Compared to even a few days ago when I wrote this, I like Harris even more now.  Boston journalist Greg Bedard makes it sound like Harris will likely win that RB1 job even with Michel healthy now.

Points: 0

#8 by Lost Ti-Cats Fan // Aug 29, 2020 - 7:00pm

Who wants to venture a guess on how many times we see NE line up Newton, Michel, Harris and Burkhead in the backfield ... plus White split out wide.

Points: 0

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