Does Size Matter For Running Backs? 2018 Update

Seven years ago, I studied NFL statistics to determine whether larger running backs are more effective in short-yardage situations. As a result of that study, Does Size Matter for Running Backs?, I suggested that "a model short-yardage runner is 69 inches tall and weighs 210-215 pounds," but my research was limited by small sample sizes. Today, I'm revisiting that study with another 70 player-seasons in the sample.

For every season from 1991-2017, I looked at the top 10 rushers that year, slicing and dicing their statistics to see how height, weight, and Body Mass Index (BMI) might play a role in short-yardage success. I looked at top-10 rushers so that the study compares good players to other good players, and 1991 is a good starting point because that's the year the NFL began keeping first down data for individual players.

'91 is also post-Fridge, meaning that most linemen consistently and dramatically outweighed most running backs at this point, which hadn't been true as recently as the early '80s, with heavyweights like Earl Campbell and John Riggins bulldozing smaller, athletic defensive linemen like Fred Dean, L.C. Greenwood, and Alan Page. The game and its players have evolved in a way that limits the impact of larger backs, especially in obvious short-yardage situations.

There are a lot of numbers coming up, so for those of you whose eyes get blurry at that kind of thing — or if you just can't stand suspense — being taller and heavier does not appear to help in short-yardage situations, and it may be detrimental.

The average top-10 rusher, looking at all 27 seasons, was 71 inches tall (5'11") and weighed 219.7 pounds, with a BMI of 30.6. That's about the same as Marshawn Lynch or Jordan Howard. BMI is a basic measure of the relationship between an individual's height and weight. A higher BMI indicates more weight per inch of height. Essentially, a higher BMI means a fatter (or at least more muscular) running back.

The height, weight, and BMI of the top 10 rushers has remained fairly constant over the past two decades, and the year-to-year fluctuations are small and inconsistent, so they appear to be coincidence and normal variation rather than patterns or trends.

I examined relationships between these three size factors and a number of statistical categories, including: rushing yards, rushing TDs, rushing first downs, and percentage of rushes yielding first downs. Note that the NFL counts a touchdown as a first down, so TDs count in both categories. In all cases, the height and weight I used are those given on a player's page.


I am less confident in this than I was in the first edition of this article, but the optimal height for a goal-line running back is probably 5-foot-9. I broke the 270 RB seasons into seven groups:

(1) less than 5'9" (20 seasons, includes Barry Sanders, Maurice Jones-Drew, and Devonta Freeman)
(2) 5'9" (28 seasons, includes Emmitt Smith, Priest Holmes, and Frank Gore)
(3) 5'10" (54 seasons, includes Marshall Faulk, LaDainian Tomlinson, and Kareem Hunt)
(4) 5'11" (70 seasons, includes Terrell Davis, Chris Johnson, and LeSean McCoy)
(5) 6' (27 seasons, includes Edgerrin James, Ahman Green, and Ezekiel Elliott)
(6) 6'1" (50 seasons, includes Ricky Watters, Adrian Peterson, and Le'Veon Bell)
(7) more than 6'1" (21 seasons, includes Eddie George, Steven Jackson, and Matt Forte)

The players mentioned are examples, not the only top-10 RBs of that height. Group 2, the 5'9" players, outperformed the other groups in every short-yardage category: rushing TDs, first downs, and first down percentage.


Barry Sanders supplies eight of the 20 seasons in Group 1, and Emmitt Smith is responsible for eight of the 28 seasons in Group 2, skewing the results for those two groups. In search of a more meaningful sample size, I combined both heights into a 48-season sample of all the RBs under 5'10". I did the same for all RBs over 6 feet tall, since nearly half (9/21) of the over-6-foot-1 category is Eddie George or Steven Jackson.


These data are less dramatic than the original study from 2011, but a note of caution about tall goal-line backs, particularly those over 6'1", still seems potentially relevant. All things being equal, I would want my team to use a short-yardage back who is under six feet tall.


For the categories tracked, a weight between 206-225 pounds appears to be ideal. Lighter-weight RBs outperformed the heavier backs in most categories, but in the statistics linked to short-yardage performance, neither very light nor very heavy runners equaled those near the middle. I sorted players into five weight classes:

(1) 205 lbs. and below (30 seasons, includes Barry Sanders, Tiki Barber, and Jamaal Charles)
(2) 206-216 lbs. (86 seasons, includes Emmitt Smith, LaDainian Tomlinson, and Marshawn Lynch)
(3) 217-225 lbs. (70 seasons, includes Edgerrin James, Adrian Peterson, and Le'Veon Bell)
(4) 226-235 lbs. (57 seasons, includes Eddie George, Shaun Alexander, and Arian Foster)
(5) over 235 lbs. (27 seasons, includes Jerome Bettis, Steven Jackson, and Eddie Lacy)


Emmitt Smith is listed at 216 lbs., his weight with the Cardinals at the end of his career. Smith played most of his career 5-10 pounds lighter than that, and he is the only player in the study listed at 216. I thought it was more accurate to include him in a 206-216 group than to slavishly adhere to multiples of five.

The Emmitt category performs best in every stat except yards per carry, which is not associated with short-yardage success, and first down percentage, where the lightest weight group is fractionally ahead (22.54% to 22.46%). It is interesting to note that first down percentage consistently drops as weight rises (rushing yardage does as well). Based on these data, I would suggest that the low TD totals of the lightest group owe more to usage bias than to any performance-related shortcoming. Even Barry Sanders, who was regarded as a short-yardage liability late in his career, led the NFL in TDs two of his first three seasons.

I also evaluated two alternate takes, using weight categories with larger samples:


The table above simply compresses the two lightest categories and the two heaviest, creating samples of 116 seasons, 70 seasons, and 84 seasons. The differences are not large, but they appear to slightly favor lighter-weight RBs.


There are 62 in the lightest group, 95 seasons in the middle, and 113 in the heaviest group. Touchdowns clearly favor the Goldilocks category, while first down percentage drops as weight increases (mirroring the data above).


The formula for BMI is kilograms divided by (meters squared): BMI = kg/m². Or, for us heathens in the U.S., multiply your weight in pounds by 703 and divide by the square of your height in inches: BMI = (703 * lbs) / in². Higher BMIs indicate more weight per height. A healthy BMI is usually between 18.5-24.9, though this is acknowledged to be inaccurate for athletes with high muscle mass.

I used five groups here:

(1) below 29 (34 seasons, includes Ricky Watters, Adrian Peterson, and Chris Johnson)
(2) 29-29.9 (75 seasons, includes Thurman Thomas, Edgerrin James, and LeSean McCoy)
(3) 30-30.9 (67 seasons, includes Barry Sanders, LaDainian Tomlinson, and Marshawn Lynch)
(4) 31-31.9 (42 seasons, includes Emmitt Smith, Priest Holmes, and Shaun Alexander)
(5) 32 and over (52 seasons, includes Jerome Bettis, Ricky Williams, and Frank Gore)

As you might expect, the 31s blow away the pack. Smith, Holmes, and Alexander all set single-season TD records in the last 27 years, and this group is clearly and dramatically the best in the short-yardage categories. Devonta Freeman, who tied for the league lead in 2015, is a more recent example of an elite runner in this BMI group.


It seems apparent that the optimal BMI for a short-yardage back is something close to 31.5. The other groups are all roughly equal, and all far below the 31.x-BMI group.


Examining height, weight, and BMI, each category had a single group as the clear leader: 5-foot-9, 206-216 pounds, and especially a BMI between 31-32. This matches or very nearly matches: Emmitt Smith, LaDainian Tomlinson, Priest Holmes, Frank Gore, Earnest Byner, DeAngelo Williams, Devonta Freeman, Mark Ingram, Barry Foster, Steve Slaton, and Kareem Hunt.

Short-Distance TDs

The top 10 in rushing TDs of 1-2 yards, since 1991:


Hold the presses! This doesn't look like 5'9" is an ideal height for RBs. Nine of the 10 players are taller than that!

That's because most RBs are taller than 5'9". Only 48 of the 270 seasons included were by a running back that short — and a third of those 48 seasons are just Emmitt and Barry. Players that short seldom even get a chance in the NFL, or they're forced into part-time roles and leave the game in goal-to-go situations. A team that has a choice uses Tons of Fun in that situation.

When short RBs get a chance, however, they prove themselves over and over. DeAngelo Williams is about 5-8½, and he spent his prime paired with a stereotypically "big back" who got most of the goal-line work, but Williams led the NFL in TDs the only year he got at least 220 carries. Priest Holmes (5'9") set a single-season TD record. Maurice Jones-Drew is only 5'7", but he scored double-digit TDs in four of his first five seasons. Devonta Freeman is 5'8", and he's rushed for double-digit TDs in both of his seasons as a full-time player, with a first down percentage north of 25%. Smith, of course, is the all-time leader in rushing TDs, one of the greatest short-yardage runners of all time.

The average size for the leaders in 1-2 yard TDs corresponds almost exactly to the averages of all top-10 rushers: 71 inches tall (5'11"), 219.7 pounds, 30.6 BMI. The difference is about half a pound.

The Ideal Size

The takeaway from this data isn't that smaller runners are more effective in short-yardage situations, as I implied in the previous version of this study. It's even simpler: size doesn't matter.

While the data do suggest that lighter runners create first downs more often, and that a BMI in the 31-31.9 range has produced some great goal-line backs, those data simply aren't very compelling. More significant is what the data clearly does not show: any evidence — any evidence at all — that taller or heavier RBs are more effective at generating first downs and/or touchdowns. In almost all cases, a team's best goal-line runner is its best running back, regardless of size. Subbing out your 210-lb. superstar for a less dynamic 240-lb. bulldozer is simply not good strategy. Even elite 240-pounders, like Michael Turner and Steven Jackson, are no more effective in short-yardage situations than elite 210-ers, like MJD and Shady McCoy.

Domination of the game (and the goal line in particular) by giant RBs has noticeably diminished over the past several decades. I would suggest that the primary reason for this is the explosion of size among linemen. Remember when Refrigerator Perry was a punch-line, a guy so fat it was comical? Now every team has someone that big. It used to be that a John Riggins or Earl Campbell could get a head of steam and bowl over linemen who weighed about the same as he did. But now, send a 240-lb. RB crashing into a wall of 320-lb. refrigerators, and he's not going to get past them.

I would posit that the performance of the offensive line is probably the most important factor in straight-ahead rushing attempts, and that even a big, strong RB is very limited in his capacity to create opportunities without a strong push from his blockers. A faster RB who works outside, or presents the threat of an outside run, may be less handcuffed by his blocking opportunities, and presents more problems to a defense. Send in the tank, and the defense knows it doesn't have to defend against an outside run. A more nimble back forces the defenders to spread out.

When LaDainian Tomlinson set the single-season TD record — a record that will probably never fall in a 16-game season — I thought his vision and quick first step were his most important assets. He wasn't bowling defenders over, he was finding weaknesses and beating them to a spot.

Running backs can't run through holes if the blockers in front don't make them. The most successful short-yardage runners in today's game threaten as much with their agility and balance as their power, and probably more than anything with their vision and intelligence. A good running back will do well on the goal line, too, regardless of size. An increasingly popular trend involves increasing the size of the blocking back rather than the ball-handler, for instance by using a 310-lb. defensive tackle at fullback. I'm not convinced that makes a positive difference, but it's a better idea than replacing your best RB with a big slow guy just when you really need a good play.

It probably was true at one time that larger backs were more effective at picking up 3rd-and-1, but that was a long time ago. If you still believe, in 2018, that your best bet on the goal line is the 240-pounder who snuck out of the locker room for a hot dog at halftime, I don't know what game you're watching. Is Howard Cosell announcing?

The best goal-line runner is your best running back, period. He doesn't have to be huge, and it might be preferable that he isn't.

Possible Biases

That's basically it, but if you're interested in stats, you might want to keep reading about how the numbers presented above might be misleading. If that doesn't sound interesting, you can quit while you're ahead and probably won't miss anything important. Thanks for stopping by.

The numbers don't lie, but that doesn't mean they necessarily tell us what they appear to tell us. The four most important potential biases that seem likely to me are: (1) unequal opportunity, (2) weight variance over a player's career, (3) usage by good teams and bad teams, and (4) possible issues with sample size.

1. Bigger RBs get more short-yardage opportunities than smaller RBs.

Conventional wisdom dictates that a big, heavy back (like Jerome Bettis or Eddie Lacy) is best-suited to short-yardage situations, and that a lighter back (like Terrell Davis or LeSean McCoy) is not a good choice for those situations. Of course, Davis (210 lbs) and McCoy (210) and Jamaal Charles (199) and Terry Allen (208) and Marshall Faulk (211) and Priest Holmes (213) and LaDainian Tomlinson (215) and Marshawn Lynch (215) and Barry Sanders (200) all led the NFL in TDs, which Bettis (255) and Lacy (250) and Jamal Lewis (245) and Michael Turner (244) and Larry Johnson (235) and Eddie George (235) and Deuce McAllister (232) never did.

I believe the disadvantage of heavier RBs is even greater than it appears from this data, because they get many more goal-line opportunities than lighter RBs. Tiki Barber, listed at 205 lbs., was a very good short-yardage runner, but the Giants routinely subbed him out for Ron Dayne (245) and Brandon Jacobs (264). I remember thinking at the time that it was crazy. Dayne was a disaster, and Jacobs, especially early in his career, wasn't much better. But the Giants regularly removed their best running back from the game in the most crucial situations. That's a little like subbing out Drew Brees for someone with a stronger arm on 3rd-and-6.

Barber scored more rushing TDs of over 10 yards (20) than rushing TDs of 1-2 yards (18), because the Giants rarely gave him the ball in short yardage. Some of you may remember that Barber had a fumbling problem, and wonder if the Giants kept him out of goal-line situations because they were afraid he'd lose the ball. Only 32 of Barber's 53 career fumbles came on rush attempts. The others were receptions or punt returns, where fumbles are more common. Barber fumbled less often per carry (1.44%) than Jacobs (1.67%), and in 2005, he actually had the fewest fumbles (1) of any top-10 rusher.

Barber is just one example. In 2005, splitting time with Bettis, Willie Parker scored TDs of 10, 11, 37, and 80 yards. The next season, with Bettis retired, he scored from 1, 1, 1, 1, 3, 3, 3, 3, 3, 4, 8, 9, and 41. Obviously he could handle short-yardage, but he lost opportunities because he played with a guy who outweighed him by 45 pounds. The same thing happened to Chris Johnson, who in his 2,000-yard season regularly left the game so LenDale White could stumble into a wall of defenders.

Just this past season, Week 7, Bengals at Steelers... on 4th-and-1, Pittsburgh subbed out Le'Veon Bell for 240-pound Terrell Watson. Bell had 134 rushing yards and 192 total yards in that game — he was on fire. Watson plunged up the middle and failed to make the yard, turning the ball over to Cincinnati. A critical play like 4th-and-1 is when you're so grateful to have an extraordinary talent like Le'Veon Bell, and instead the Steelers put him on the bench.

When we approach the question of RB size, it's important to acknowledge that the usefulness of data is limited by the way coaches perceive and utilize players based on outdated preconceptions about size.

This problem is somewhat less common today, but smaller guys often don't get a chance to prove themselves in short-yardage situations. Their TD statistics are poor not because they're bad at picking up 3rd-and-1 or 4th-and-goal, but because they're seldom in the game on 3rd-and-1 or 4th-and-goal. Thus, the lightest backs are probably even better at short-yardage than their stats suggest, and the big guys probably a little worse.

A player's weight can vary over his career.

As a rookie, Clinton Portis weighed about 190 lbs. He rushed for 1,500 yards, with a 5.5 average and 15 TDs. The next season, almost 1,600 yards, 5.5 average, 14 TDs. Then he got traded to Washington, and bulked up to 220 in an effort to handle increased workload. For what it's worth, all his career highs were set in those two seasons, but that's not the point — on every line of this study, Portis is 5'11", 219 lbs. That means that in '02 and '03, his weight listing is off by almost 30 lbs., and that the results are not 100% accurate.

Similarly, Emmitt Smith is listed at 216. He put on weight at the end of his career, but was below 210 in the '90s. In this study, Jerome Bettis is 255 lbs., because that's what his page shows, but in his prime, Bettis barely weighed 240. Late in their careers, many players compensate for lost speed with extra size and strength, so again, most RBs are probably listed weighing more than they did in their primes. Some are even listed at different heights. Fred Taylor, six feet as a rookie in 1998, was later listed at 6'1".

Bad teams are more likely to use unusually big or small RBs than good teams.

Most teams, if they have a choice, use a running back close to average size: somewhere between 5'9" and 6'1", 205-235 lbs. Players who fall outside that range are most likely to play only if the team is desperate: if there are no other good running backs on the roster, or if injuries force him into action. That's how Justin Forsett, a 195-lb. emergency option, became a 1,266-yard rusher and Pro Bowler for the Ravens in 2014. Players who are too short, too tall, too heavy, too light, usually begin their careers as part-time players: special teamers, third-down backs, goal-line specialists, fullbacks. If the team already has an Emmitt Smith or Adrian Peterson, they might not carry the ball at all.

Bad teams sometimes have no choice but to put these players in the lineup, and often, they pleasantly surprise. But a bad team with a good running back is still a bad team. It won't score very many touchdowns, and it especially won't score many rushing touchdowns. It won't get a lot of first downs, and it will have a poor first down percentage. Thus, the size outliers — the very big and the very small — might be better than their low TD and first down numbers suggest.

Possible issues with sample size.

In any study like this, you have to balance precision with certainty. A small group thats fit a certain height or weight range, perhaps as few as 15 or 20 players, may not be terribly meaningful. On the other hand, a larger group — say 135 seasons — eliminates that uncertainty, but with only two groups, you're lumping together as "similar" vastly different players. We could split weight at 220 lbs., yielding groups of 147 seasons and 123 seasons: nice, big samples. But now we're putting Darren McFadden and Ryan Mathews in the same category as LeGarrette Blount and Eddie Lacy. That's just not a valid comparison. When we talk about big backs, we don't mean guys like McFadden. And for that matter, we usually don't mean players like 215-lb Marshawn Lynch and 217-lb Adrian Peterson when we talk about small backs. By the same token, we don't think of 215-ers like Emmitt, LT, or Garrison Hearst when we refer to big backs.

Precision versus sample size is a trade-off. Two-hundred-seventy seasons are a lot, and I think there's a decent balance in most of the data sets presented here, but it's not perfect.

To the extent the data presented here may be misleading, I think it's more likely to underrate the short-yardage ability of smaller players and to overstate the same ability in bigger guys. At the same time, it's important to recognize the way players like Barry Sanders, Emmitt Smith, and LaDainian Tomlinson — each of whom contributes eight seasons to this study — have outsized influence in relatively small data samples. The conclusions I've drawn in revisiting this topic are slightly different than those I drew seven years ago, partly because the hyperbolic influence of players like Emmitt diminishes as the sample size grows.

That said, I wish coaches would just give the ball to their best players, regardless of size, in critical situations. My findings suggest that their fans should wish so as well.

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