Larry Fitzgerald is built like a power forward. He's tall, wide, and has Tracy McGrady-like hops.
Ask any defensive back what it takes to stop Fitzgerald, and he'll tell you one thing. Better yet, ask any defensive back what it takes to be successful in the league, and he'll tell you one thing. He'll tell you that it really has little to do with his speed, knowledge of the game, or coverage ability. To be a good defensive back you need a good pass rush.
You'll surely recall last year's Super Bowl. Tom Brady, with three rings, was poised to get his fourth, justifying the comparisons to Joe Montana. The Patriots' addition of Randy Moss made this very likely. But a funny thing happened: A group of guys named Strahan, Tuck, Umenyiora and Robbins so thoroughly harassed, interrupted and beat up on Brady that he couldn't throw the ball with any consistent degree of success. It's just a simple law of the game: no man can effectively throw the ball while other men are knocking him on his ass.