The difference between a good defense and a great defense relies heavily on the safety position. Every corner needs to have absolute trust in the safety behind him when he breaks coverage of a wide receiver. Some of the most successful blitz packages involve safeties.
The safety, whether free or strong, is the eye of the defense. He is the quarterback of the backfield. In 2010, some of the most successful defenses included a top safety (Chicago, Baltimore, Pittsburgh, etc.) When those players had a bad day, their opponents had field day on the secondary. Heading into 2011 (hopefully), there has been some signings of big name safeties that could help some struggling secondaries become great ones. These are some safeties that had a good season last year and are hoping to build on it, or are looking to rebound from an injury.