Size Does Matter: How an NFL Player's Height and Weight Affect Performance

Every year, it seems like a few talented college players are being snubbed from the NFL because their measurables, in NFL draft speak—height and weight, for example—are poor. To wit:

• Missouri quarterback Chase Daniel finished fourth in the Heisman Trophy voting in 2007—the second-highest ever for a Tiger—and finished his college career with the most offensive yardage in Missouri history. He had over 13,000 total yards in his three full years as a Tiger, including over 4,300 passing yards in both his junior and senior seasons.

His completion percentage was 72.9 percent in his final season, in which he also had 39 touchdowns and 18 interceptions.

But scouting reports said that Daniel, measured at 6'0" at the Scouting Combine, "lacks ideal height for an NFL quarterback." Daniel went undrafted in the 2009 NFL Draft and is currently fighting for the No. 3 quarterback spot on the Washington Redskins.

• Northern Illinois running back Garrett Wolfe’s worst college season was his junior season. He gained a measly 1,580 yards on the ground with a dismal 16 touchdowns on 243 carries, pathetic numbers for a man who also missed three games due to injury.

Sarcasm aside, Wolfe gained over 1,600 and 1,900 yards in his other two seasons (the latter of which led the NCAA), but at 5'7" and 186 pounds, Wolfe was drafted at the end of the third round to the Chicago Bears.

He hasn’t been given much opportunity to shine at all, with 46 career carries in two seasons in the NFL.

• The prototypical small guy, at 5'9", Wes Welker failed to garner much attention after high school. A week after signing day, Welker received a scholarship from Texas Tech when one of the Red Raiders’ projected signees chose a different school.

In his four-year career at Texas Tech, Welker had 3,475 total yards from scrimmage (rushing and receiving) with 23 touchdowns. His eight career punt return touchdowns set an NCAA record (since tied).

Welker went undrafted in the 2004 NFL draft; he signed with the San Diego Chargers but was ultimately cut after Week One.

Nevertheless, Welker showed that small players can succeed in the NFL. After breaking onto the scene in 2006, with 687 yards on 67 receptions for Miami, he was traded to the Patriots. Welker ended up with a league-high 112 catches in 2007, followed up by 111 in 2008; he had over 1,100 yards as well each of those two years.

Others, such as 6'0" Drew Brees—who, among many other accomplishments, threw for 5,000 yards in 2008—have proved that, when given the chance, size doesn’t matter.

In this article, I’ll be testing the effects of height and weight on seasonal and career production, split up by position.

Do taller quarterbacks have a higher completion percentage, on the notion that they can see over the line of scrimmage? Do taller wide receivers have an advantage over smaller receivers when it comes to yards and touchdowns?

As always, my data comes from Pro-Football-Reference.com. Unfortunately, I could only find height and weight data in the college section of P-F-R, so I went through the 212 colleges with 20 or more guys who played in the NFL and collected height and weight data from there. This gave me height and weight data for all but 898 of the more than 10,000 player seasons since 1980 (and career data for all but 227 of the more than 2,300 player careers).

Now, I don’t know the source of P-F-R’s height and weight data; I presume it is the numbers given out by each team. This may have some drawbacks (smaller players will sometimes get a boost to their height or weight, for example), but in general it works.

The first measure of correlation between measurables and production is, well, correlation.

Correlation shows the relationship between two variables in a number between negative-one and one.

The more related two variables are, and the more the graph between the two looks like a perfect line, the closer to one or negative-one the correlation is; a positive number represents a positive relationship—that is, as one stat goes up, so does the other—and a negative number represents a negative relationship—when one variable goes up, the other goes down.

Since that probably made no sense, take a look at this graph, which shows the correlation of several sets of data. If, say, weight and completion percentage form a straight line rising to the right, the correlation will be one. If they form a straight line rising to the left, the correlation is negative-one. And if there’s no relationship whatsoever (a scattered mess), it’s zero.

I took the career statistics of every player post-1980 (with 300 career pass attempts, 100 rush attempts, or 100 receptions) and plotted them with their height and weight. Here are the results.

 
In this scenario, a positive correlation means that taller or heavier players have better statistics than shorter, lighter players, aside from interceptions, which is the other way around.

We see a small positive correlation between weight and most passing stats (all those except yards per attempt). In each case, as weight increases, the stat in question rises accordingly (or drops, in the case of interceptions).

The largest correlation between height and any passing statistic is, interestingly, between height and completion percentage, though the correlation is negligible.

There’s not much correlation between measurables and rushing statistics, with the obvious exception of weight and rushing touchdowns. Heavier running backs tend to be the ones who score the most touchdowns, which is what we expected.

Then there’s the wideouts. There’s a very strong correlation between weight and yards per catch, at -0.653, which means that, somewhat counter-intuitively, shorter wide receivers have more yards per catch than taller receivers.

The correlation is even more staggering when you consider that there were fewer than 100 unique weights for the more than 400 receivers in the study; it rises to -0.819 when you only look at the average yards per catch at each of those unique weights.

This, in turn, brings up a good point: If there are so few unique weights or heights (of which there were 14 between those 400 receivers), then looking at correlation coefficients won’t show the real relationship between measurables and on-field production.

In other words, in order to look at this relationship (or non-relationship), we must group receivers based on their height and weight and look at the statistics from the totals in each bin of receivers. I did this for each position, making sure each bin had a sufficient number of players in it (at least 40 or so).

Here are the results for quarterbacks. All heights are in inches and all weights in pounds.

 
A quarterback’s performance tends to be highest when the passer is 74 inches tall (6'2"), but this could also be contributed to the fact that, either coincidentally or not, Brett Favre, Joe Montana, Steve Young, and Kurt Warner were all 74 inches.

Removing that particular height, quarterback rating increases at each height increment. As well, completion percentage for the shortest quarterbacks is lower than any other height, a full point lower than the tallest players’ completion percentage.

That said, there’s no real pattern between height and completion percentage beyond that.

The largest correlation comes from weight and interception percentage. Interceptions decreased each time weight increased, with a steep decline from quarterbacks weighing over 215 pounds.

I’m hypothesizing here, so bear with me, but heavier quarterbacks may be more inclined to take a sack under pressure, whereas lighter ones will instead throw the ball up to evade a sack.

I don’t have sack data, so I can’t test this hypothesis. This may be, however, just a correlation/causation issue—in other words, there may be another outside factor affecting interceptions.

In addition to looking at the average statistics at each height or weight, I also looked at the chance of a "great" season by looking at the odds of finishing in the top quarter in that particular stat.

I only included seasons where the quarterback had 350 pass attempts. Here are the results.

 
Does this confirm the myth? Again, excluding 6'2″ quarterbacks, completion percentage increases each time height does as well.

Taller quarterbacks also have higher odds of reaching the top quartile in yards per attempt than their smaller counterparts; 6'5" passers reach that twice as often as 6'1" quarterbacks.

We also see that the chance of having a great season in touchdowns per attempt decreases each time weight increases. We didn’t see this trend in the first quarterback graph, however, so I’d say that that is just a mere coincidence.

Backing up our previous conclusion, the probability of throwing for 12 or fewer interceptions more or less increases as weight goes up.

I then examined the predictive power of height and weight. I looked at all QBs who stayed with the same team and had 300 pass attempts in three straight years, then ran a regression using past two years of data plus height or weight to predict the third year.

For example, quarterback rating is equal to 0.373 * (last year’s rating) + 0.153 * (rating two years ago) - 0.684 * (height) + 91.246. That means the difference between a 73-inch and 77-inch quarterback’s passer rating is equal to (77 - 73) * (-0.684), or 2.74 points of quarterback rating, favoring the smaller passer (the coefficient for height is negative).

Weight affects passer rating by 1.15 points, favoring heavier QBs. Smaller QBs have an 8.82-fantasy-point edge over taller QBs over the course of 450 pass attempts, though weight had a much lower affect on fantasy points (2.21 points, favoring heavier QBs).

Completion percentage wasn’t changed by height or weight much at all. Passing yards, touchdowns, and interceptions favored smaller quarterbacks, yet touchdowns and interceptions also favored heavier QBs.

Almost every stat favors both small (height-wise) and heavy quarterbacks. I then ran the same test using body mass index, or BMI, which is an easy-to-use statistic that identifies a player as underweight, normal, or obese. What we want to see is an edge toward obese players, guys who are heavy yet small in stature.

In fact, we see nearly the same results as before. The difference between a 73-inch, 200-lb. and a 73-inch, 230-lb. quarterback all favor the beefier passer: an edge of 3.16 points on quarterback rating, 8.39 fantasy points, a minimal change in completion percentage (one-half of one percent), 13.89 yards, 1.09 touchdowns, and 1.91 fewer interceptions.

It should be noted, however, that those 8.39 fantasy points were the difference between the Nos. 13 and 17 quarterbacks last year in terms of fantasy points.

So, when you’re in the late rounds of your draft, and you see Eli Manning and David Garrard both available, take the time to think about BMI: The difference between Manning’s BMI (26.5) and Garrard’s BMI (32.2) equates to a whopping 12 fantasy points in 450 attempts.

Now we'll move on to the running backs. Here are the average stats at each height and weight group.

 
There’s a very strong correlation between height and yards per carry. We see a downward trend in yards per carry as height increases, with the exception of the jump from 74 to 75 inches tall.

This pattern is backed up by the relationship between weight and YPC; for each 10-pound bin, there is an average drop of 0.06 yards per carry (15 to 20 yards in a season for a full-time back).

In fact, the difference between the YPC of the 68- and 73-inch backs (more than one-third of a yard) equates to 90 to 100 yards over the course of a season—the difference between the 11th- and 17th-ranked backs in terms of rushing yards last year, mind you.

There’s no relationship, on the other hand, between height, fantasy points, and touchdown percentage.

As well, the correlation between weight and rushing touchdowns is small but apparent, as touchdown percentage increases somewhat as does weight. The difference in touchdown percentage between the small and heavy backs equates to two touchdowns in a full season, roughly the difference between the 12th- and 17th-ranked backs in terms of fantasy points last year (an average No. 2 back as opposed to a borderline No. 1 RB).

Let’s compare the above table with the one below, which shows the probability of finishing in the top quartile. I included only those backs with 200 rush attempts.

 
There’s a slight correlation between height and rushing touchdowns, taking out the jump (again) from 74 to 75 inches, that suggests touchdowns fall as height increases.

We also see a very interesting pattern when looking at weights and fantasy points. There’s a downward trend when it comes to the odds of finishing in the top quarter as weight increases. Why?

The answer is fantasy points. Because of their subjective weights (10 yards for one point, six points for a touchdown), the average running back in the sample had 70 percent of his fantasy points come from total yards, which, obviously, benefits the small backs with a lot of yards but just a few scores.

Continuing on with the predictive value of height and weight, the difference between a 5'8" and a 6'3" running back is 5.9 fantasy points in 250 attempts—an advantage to the smaller back by less than 51 yards and three-tenths of a touchdown. (Yes, the coefficient for rushing touchdown percentage was negative, but so small that it’s negligible.)

When looking at weights, we see that the lighter backs have a 2.39-fantasy point and an 18-yard edge over their heavier counterparts, while the heavier rushers have a 0.55-touchdown difference.

Unlike quarterbacks, height and weight seem to show the same conclusions for running backs, that shorter, smaller backs perform better. Thus, looking at BMI—which divides weight by height—will essentially neutralize the height/weight issue.

(This, in fact, is true, as the difference between the highest and lowest backs in BMI is less than one fantasy points, five rushing yards, and one touchdown.)

For running backs, we need to multiply height and weight, to combine them into one statistic.

When we do this, we find that the difference between a 68-inch, 200-lb. and a 75-inch, 250-lb. back is 5.79 fantasy points and 46 yards in favor of the lighter back and less than four-fifths of a touchdown in favor of the heavy runner.

Nevertheless, this is what we expected in the first place: smaller backs get the yards, and the bruisers get the scores. In terms of fantasy points, the differences in rushing yards and touchdowns are nearly equal, but the five-plus advantage in fantasy points for the small guys comes from their receiving.

In addition, another thing that may benefit the smaller rushers is the fact that yards may be a greater function of skill than touchdowns, considering that it only takes a good quarterback to move the offense into the five-yard line for a back to get a score.

Think about getting a small, fast runner like Leon Washington instead of a bruiser like Le’Ron McClain or Tim Hightower heading into the latter rounds of your draft. Washington’s receiving, as well as the fact he may get a few gratuitous touchdowns, may vault him over McClain or Hightower.

Now, let’s look at receivers—both wideouts and tight ends. Here are the statistics of each group of receivers.

 
There’s a clear correlation between measurables and production for wide receivers, and it’s not what you may have thought: shorter, smaller receivers perform better than taller, larger wideouts.

Shorter receivers have a higher yards-per-catch than taller receivers, though the pattern isn’t as noticeable as the relationship between weight and YPC; we see that yards-per-catch falls each and every time weight increases. The difference between the lightest and heaviest wideouts is 4.37 YPC, which equates to over 300 yards for a starter with 70 catches.

Keep in mind that those extra 30 fantasy points were the difference between the Nos. 8 and 19 receivers in terms of fantasy points, and the 300 yards were the difference between the Nos. 6 and 21 receivers in receiving yards last year.

There is, however, a slight positive trend regarding height and touchdown percentage, in that taller receivers have a small benefit over shorter ones. But the effect of height on touchdowns doesn’t cancel out yards per catch—smaller receivers still have more fantasy points per catch than taller wideouts.

That doesn’t hold steady, though, when looking at weight and touchdowns; there’s no relationship whatsoever between the two variables.

Now we'll examine the chance of producing a season in the top quarter, including only those receivers with 60 receptions.

 
Looking at the table, we don’t see any trend based on height and fantasy points. But when we split it up based on groups of three, we do: Wide receivers less than 71 inches tall finished in the top quarter of fantasy points 27 percent of the time, compared to 25.5 percent for wideouts between 72 and 74 inches and 22.5 percent for those greater than 75 inches.

Doing this for both yards per catch and touchdowns per catch, we see the obvious—YPC goes down as height increases, and touchdowns goes up as height goes up.

(By the way, the difference in those odds in YPC between the tallest and shortest receivers is 8.2 percent, while that number is 2.3 percent for touchdowns per catch. This suggests that it’s easier for shorter receivers to have a good season in touchdowns than it is for taller receivers to have a good season in terms of yards per catch.)

There’s a loose correlation between weight and yards per catch, while there’s not much relationship between weight and touchdowns.

The receivers above 241 pounds were all tight ends, so don’t look into the zeros too much.

Looking now into the forecasting power of height and weight for receivers, we see that, for receivers with 60 receptions in three straight years for the same team, height affects yards by only 7.86 yards in 70 receptions—benefiting smaller wideouts—while it affects fantasy points and touchdowns by less than one-fourth—both benefiting taller receivers.

Onto weight, we find that 180-pound receivers have a 6.55-fantasy-point and 37-yard edge over 230-pound receivers, as opposed to the 0.45-touchdown advantage the heavier receivers have.

It appears that height multiplied by weight will include both of those measurables into one statistic and would be a better indicator than BMI, but that’s wrong; I did these tests with both stats, and BMI affects production much greater than height x weight.

The difference between a 5′ 9″, 180-pound receiver and a 5′ 9″, 230-pound receiver? A massive 16 fantasy points—82 yards and 1.24 touchdowns, both with the edge to the bonier wideout. Sixteen fantasy points was the difference between the Nos. 15 and 23 receivers in fantasy points last year.

Remember last week’s article regarding aging curves? I commented on how Ted Ginn Jr. could have a breakout season this year, as he’s turning 24.

Here’s more evidence that you should take him late in your draft: The 3.26 difference in  BMI between him and highly-touted rookie Michael Crabtree, who is being selected 20 spots ahead of Ginn overall, equates to an advantage for Ginn of seven fantasy points, 36 yards, and half a touchdown.

Be sure to look at Ginn—as well as Cardinals receiver Steve Breaston, whose BMI is even two points less than Ginn—as possible sleepers at wide receiver in your draft.