Troy Polamalu is retiring after 12 years in the NFL. Exactly how good was he in the NFL?

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 5'10â€, soft-spoken safety who stars in shampoo commercials?

The Taxonomy

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.

Need some convincing about the AV score? Here's a list of the top-five career scores: Reggie White (226), Bruce Smith (223), Ray Lewis (222), Rod Woodson (192), and Derrick Brooks (190). Still not convinced? Here's 6 to 10: Junior Seau (189), Lawrence Taylor (182), Ronnie Lott (161), Rickey Jackson (160), and Michael Strahan (160).

(For perspective, the average career AV score for all 7,495 players in the Pro Football Reference database was 17.8.)

Football's Platypus

To quantify Troy Polamaluâ€™s career performance, we compared his career AV score against all other defensive players' career AV scores. More specifically, Polamalu's score was compared to all defensive players who started their career between 1970 and 2014. Polamalu's career AV score is 117, which is the top 1% of all defensive AV scores. He's ranked 68th out of the nearly 7,500 defensive career players from the Pro Football Reference database -- that's 35 years of defensive players. And Polamalu is 68th.

One caveat to this analysis could be that, as players play in more games, they have more chances to accrue a higher AV score. Thus, there could be active players who haven't played as many games as retired players. To account for this, we built an average AV score based on the number of games for each player's career. For all defensive players who have played at least 16 games, the average AV score per game is 0.27. Polamalu is tied for 21st of all time with 0.74 AV points per game. The highest ever, by a long shot, is J.J. Watt, with 1.06 AV points per game.

As of the end of the 2014 season, Troy Polamalu is the 12th-ranked safety and second-ranked strong safety ever, right behind another Steeler â€“- the Steel Curtain defense's strong safety, Donnie Shell.

Using AV Score as the determining factor, we ranked Polamalu against the all-time greats.

Player All time Defensive Player Rank All time Safety Rank All time Strong Safety Rank Donnie Shell 58 11 1 Troy Polamalu 68 12 2 John Lynch 70 14 3 LeRoy Butler 85 15 4 Ken Houston 107 17 5 Carnell Lake 114 19 6 Steven Atwater 130 21 7 Dennis Smith 130 21 7 Darren Woodson 147 23 9 Rodney Harrison 152 24 10

Troy Polamalu's career totals and all-time rankings among all defensive players since 1970 are below:

Tackles Assists Interceptions Yards Touchdowns Sacks Total 581 197 32 398 3 12 Overall Defensive Rank 205 85 108 168 140 809

Can We Just Swoon for a Bit?

Let's talk visuals. As if one could call watching giant men tackle each other "boring", Troy didn't lull us to sleep like the San Antonio Spurs' offense. Easily spotted by the flowing locks billowing out the back end of his helmet (which undoubtedly contained all of his strength), he zoomed across the secondary like a hungry lion. Remember when he superman dove over both offensive and defensive lines to sack Kerry Collins at the exact moment the ball was hiked? That's stuff you couldn't do in NFL Blitz. Remember when he ran back that intercepted pass from Joe Flacco to seal the 2008-2009 AFC championship game, and every child born in Pittsburgh that year, male or female, was named "Troy"? That was amazing.

As Polamalu ends his illustrious and probably -- definitely -- Hall-of-Fame 12-year career, he leaves us with plenty of highlights and memories. He never showboated, he never argued, and he never gave less than 110%. His elegant ferocity was reminiscent of old-school football -- a dinosaur in modern times. A once in a generation player, it might be a long time before we see someone so controlled both on and off the field.