A Riddell (trademark Symbol) Pittsburgh Steelers mini helmet autographed Troy Polamalu.

Polamalu re-defined the safety position because he was one of a kind. It's not like there are youth coaches out there teaching kids to play like Polamalu because his unique skill set would be impossible to recreate. Who else could have made leaping over the line of scrimmage a signature move?

"He's one of those once-in-a-generation type of a guy, man," Pittsburgh Steelers head coach,  Mike Tomlin,  told the NFL Media at the recent NFL Annual Meeting. "He's a different guy. The way he views the game is different. The way he plays the game is different. He is unique. And I'm sure you'll see great players in that position in the future, but none will do it quite like he does it."