San Diego's defensive resurgence began last season when coordinator Ron Rivera reworked his nickel defense. He demoted 2008 first-round pick Antoine Cason and replaced him with hybrid safety Steve Gregory.
The result? The Chargers allowed less than 17 points per game after the switch, this after giving up more than 27 points per contest through the first five weeks.
Now, the nickel defense is undergoing another wholesale makeover. Cason moves from dime back to starting corner, taking over for the departed Antonio Cromartie. The Chargers' coaches believe Cason is better equipped to play outside, away from the traffic he struggled to sort through last season.
Also, Gregory will cede his nickel back position to one of San Diego's free agent acquisitions, either Nathan Vasher or Donald Strickland. That should help from a coverage perspective, although it remains to be seen if Vasher or Strickland can be successful blitzing from the secondary, something Gregory and Paul Oliver did with regularity last season.
The stakes are high in the Vasher-Strickland showdown, as the loser will likely fall all the way out of the rotation. That's because the Chargers are incredibly deep at safety, so much so that at least one talented player won't make the final 53-man roster. This means San Diego's sixth and seventh DBs will be safeties, not corners.
Regardless, there will be some tough decisions for Norv Turner to make when it comes time to set his final roster in September. The Chargers have added three DBs since last season ended (Vasher, Strickland and Darrell Stuckey) and have cut ties with only one (Cromartie). That's bad math for any bubble players looking to extend their stays in Southern California.
That is when the decisions get sticky. Turner must choose between youth and experience. Between special-teams prowess and veteran depth. Between known commodities and unknown potential.
By the time it's all said and done, San Diego's secondary will look much different in 2010 than it did in 2009. Whether that's a good thing or a bad thing will depend on the performance of a nickel defense that will take a different shape for the third time in two seasons.
Michael Lombardo is a member of the Pro Football Writers of America and a long-time contributor to the Scout.com network. His analysis has been published by the NFL Network, Fox Sports and MySpace Sports. He has followed the Chargers for more than 15 years and covered the team since 2003. You can see more of his updates by following him on twitter.