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

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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.

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