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# 3 Numerical Fun Facts About NFL Football

What do uniform numbers tell you about NFL players? How can you estimate how fast a wide-receiver is running? How long is an average NFL game? And how much of this time is actual gameplay?

By
Jason Marshall, PhD
Episode #257

After spending the last few weeks cozying our way into the world of imaginary and complex numbers, this week we’re going to do something a little different. OK, a lot different. In celebration of the new NFL season, we’re going to run full speed into the world of NFL football.

This makes perfect sense because football is mostly about stuff like math and numbers, right? Well, perhaps not mostly. But if you take a peek just beneath all of that blood, spit, and sweat-stained artificial turf lining the fields of America’s most popular game, you absolutely will find quite a few good old numerical fun facts.

## Fact 1: What Do NFL Uniform Numbers Mean?

To kick things off today (pun totally intended), let’s talk about all of those numbers adorning the jerseys of NFL players. If you played sports as a kid, you’ll probably remember just how important it was to get the right number—probably the number of your favorite player. Sadly, if an NFL player has such a favorite number, it’s entirely possible that he will never be able to wear it.

NFL uniform numbers aren't assigned willy-nilly based upon the whims of players.

And that’s because NFL uniform numbers aren’t assigned willy-nilly based upon the whims of players. Instead, teams and players are mandated to follow a set of official NFL player jersey numbering rules put in place in 1973.

Under these rules, different positions have different assigned number ranges: Players sporting numbers between 1 and 9 must be quarterbacks or kickers. Players with numbers between 10 and 19 must be either quarterbacks, kickers, or wide receivers. Players wearing numbers between 20 and 39 must be running backs or defensive backs; those between 40 and 49 must be running backs, tight ends, linebackers, or defensive backs; those between 50 and 79 must be linebackers (but only up through 59) or offensive or defensive linemen; those between 80 and 89 must be wide receivers or tight ends; and, finally, those between 90 and 99 must be either defensive linemen or linebackers.

So now you know there’s more to those numbers than you might have thought. When you see the number that an NFL player is wearing, you’re most likely not seeing that player’s favorite number—you’re actually seeing their position.

## Fact 2: How Fast Are NFL Players?

Today’s next fun fact is based upon a simple question: How can you tell how fast an NFL player is running? Is there an easy way to do it? The answer, of course, is … absolutely! Long-time math fans may remember first hearing about this question a few years ago when we devoted an entire article to it. For today, we’re just going to quickly recap what we found.

The trick to making this estimate is to know that a speed of 10 yards per second is about the same as a speed of 20 miles per hour. This means that if you time that a player takes 1 second to run 10 yards (which is easy to see on a football field since there are big lines running all the way across the field every 5 yards), then that player must be running about 20 miles per hour. If it instead takes 2 seconds to cover that same 10 yards, his speed must be half that … or about 10 miles per hour.