Let’s travel back to 1990. On average, most defensive backs weighed between 172 and 210 pounds, most linebackers between 225 and 250 pounds, and most defensive linemen between 260 and 290 pounds. The graph below shows the amount of AV produced by defensive players at each weight in 1990:

If you look carefully, you’ll notice a few low spots on the graph. Very little AV is coming from players who weighed between 211 and 220 pounds, and also at 256 to 259 pounds. Let’s graph this another way: below, I show the percentage of all defensive AV produced by players who are X pounds or lighter. For example, about 11% of AV is produced by players 187 pounds or lighter, about one-third of AV is produced by players 210 pounds or lighter, and 34% is from players 220 pounds or lighter. The graph gets very flat between 211 and 220 pounds, indicating the lack of players in that range:

This, of course, makes some sense. There is a certain weight that is best for defensive backs, and a certain weight that is best for linebackers, but right in between those averages was a sort of no man’s land. If the average defensive back was 190 pounds, and the average linebacker 240 pounds, then a player at 215 pounds was a clunky fit for NFL defenses. He would be way too light to be an effective linebacker, but potentially too slow to fit in as a safety. As a result, there just weren’t many of those players. A 24-year-old Steve Atwater at 218 pounds was the exception, not the rule. Similarly, DE Jacob Green was becoming the last of a dying breed: he had 12.5 sacks at age 33 in 1990, while playing defensive end at a listed weight of 255 pounds.

In other words, the distribution of defensive player weight was not uniform, nor would we have expected it to be. But what about in 2017? Let’s look at the same data. Note a few things, including the fact that the Y-Axis only needs to go to 60; this means there is no one weight that has a ton of players, as we saw in 1990.

Perhaps more importantly, let’s look at the percentage graph:

There is a small flat line at around 225 pounds, but it’s shorter and less flatter than the 210-219 line. And Deion Jones, Kwon Alexander and Reuben Foster are linebackers playing at under 230 pounds, while safeties Landon Collins, Kam Chancellor, Barry Church, and George Iloka are all near 225 pounds, too.

There used to be a clearer gap between defensive backs and linebackers, shown by the relatively flat horizontal line for about 10 straight pounds in 1990 between 211 and 220 pounds.  That has been muted, and the graph above is a good representation of that.