The laws of nature are clear-cut for most predators. Catch your food, kill it, and eat it. It also helps if you’re bigger, faster, stronger, or smarter than thing you’re trying to catch.
Out of all the predators we’ve documented, classified, and studied, what is a Troy Polamalu? We know that it looks a lot like a lion, but how do we quantify the all-time greatness of a 5’10”, soft-spoken safety who stars in shampoo commercials?
Just by the eyeball test, Polamalu was a great defensive player. Maybe even one of the best. But measuring defensive performance is no easy task — it’s difficult to divvy up individual credit for things like busted coverage or preventing a big play from happening. Fortunately, however, there are some metrics that allow us to measure everything tangible for defensive players. And, as it turns out, they seem to be fairly accurate.
To represent defensive performance, we used a metric designed by Pro Football Reference known as Approximate Value (AV). The AV score is basically a single numerical value for any NFL player calculated per season. For defensive players, it’s a combination of their sacks, interceptions, defensive touchdowns, tackles, and All-Pro status. Gritty details can be found on the Pro Football Reference website.