Who's the best defensive player in the NFL?

I think that is Troy Polamalu. Look how important he is to Pittsburgh, one year they win the Super Bowl, next year he gets hurt and they miss the playoffs. That guy is stunning to watch. He shuts down every receiver he's up against, and can make amazing interceptions, that no one else can come down with. He is also very hard hitting, he can knock the ball out with his hits.