Earlier this week, we identified five offensive players GM Tom Telesco should target in free agency. And while his work re-tooling the offense will be important, it will be his upgrades on the other side of the ball that are most essential to San Diego's success.
Only one team allows more yards per carry than the Chargers and only seven teams have posted fewer sacks. That means Telesco must improve every level of his underperforming defense if his squad hopes to sniff the playoffs again any time soon.
With that in mind, here are five pending free agents on the defensive side of the ball that should be squarely on San Diego's radar.
DE Muhammad Wilkerson (Jets) - Wilkerson would cost more money than Telesco prefers to spend on one player in free agency (in the neighborhood of $60 million guaranteed), but he could be a transformational addition. At 6'4", 315 lbs., he has prototypical size and strength for a 3-4 defensive end. He is a dominant two-way force, as evidenced by his 39 tackles and seven sacks through just nine games this season.
With Wilkerson and Corey Liuget lining up at defensive end and Melvin Ingram and Jeremiah Attaochu at outside linebacker, San Diego's pass rush would suddenly change from tepid to terrifying. It would also free up Telesco to use his draft picks elsewhere, as the defensive line will have to be addressed this offseason in one form or another.
It would be out of character for Telesco to open the coffers for such a marquee player. But given how this season has played out, it would send a resounding message to all the frustrated veterans in San Diego's locker room (Philip Rivers, Antonio Gates, Liuget, etc.) that the Chargers are serious about putting a championship-contending team on the field.
DE Derek Wolfe (Broncos) - Another defensive lineman? Absolutely. Kendall Reyes and Ricardo Mathews are free agents who don't figure to return, while Sean Lissemore is a long-shot to fulfill the final season of his contract. Wolfe is a former first-round pick who is familiar with head coach Mike McCoy from their time together in Denver.
Wolfe has battled some injuries, dealing with seizures last season and a concussion earlier this year, and began the season on a four-game suspension for violating the league's policy on performance-enhancing drugs. Those factors are the only reasons the Broncos -- who are deep on the defensive line but tight against the cap -- will likely let him walk.
Wolfe posted a career-high six sacks in 2012 (McCoy's final season in Denver) and has been lights-out against the run since returning from his suspension. He could do wonders for a Chargers defense that surrenders 122.9 rushing yards per game.
OLB Tamba Hali (Chiefs) - Normally, I would not recommend targeting a 32-year-old defender in free agency, especially one who relies on his explosiveness off the edge. But Hali is an exception. He is extremely physical, intelligent and - most importantly for the Chargers - durable. He has missed just three games due to injury in his 10-year career.
The Chiefs are all but certain to let Hali walk after signing Justin Houston to a $101 million contract and spending a 2014 first-round pick on Dee Ford. The Chargers would do well to take advantage of that surplus, shoring up their own linebacker corps while weakening a division rival in the process.
Hali is not a double-digit sack threat anymore (although he averaged 11 sacks per season from 2009-2013), but he is a solid two-way player who can set the edge and collapse the pocket. He can also provide a green group with some veteran leadership, something that has been sorely missing since Jarret Johnson retired last offseason.
LB Vincent Rey (Bengals) - Rey will come with a lower price tag than the players listed above - he is earning just over $2.5 million this season in Cincinnati - but he can have a similarly significant impact. The do-it-all linebacker, who plays all three positions in the Bengals' 4-3 defense, projects as an inside linebacker in San Diego's 3-4 system.
The Chargers need help at inside linebacker, where the uninspiring Donald Butler and the injury-prone Manti Te'o have become liabilities. Denzel Perryman is in line for an increased role going forward, but more help is needed, especially if San Diego swallows hard and releases Butler, whose contract runs through 2020 and is prohibitive if voided before 2017.
Rey finished with 121 tackles last season and is on pace for 132 this year. He has also flashed some playmaking ability; in the last two-plus seasons, he has posted five sacks, 14 pass breakups and three interceptions. That production and versatility - along with his ability to dominate on special teams - make Rey a tempting target.
FS Rashad Johnson (Cardinals) - Johnson has spent his entire seven-year career in Arizona and is playing better now than he ever has. He became a full-time starter last season and responded with 92 tackles and four interceptions (remember when Eric Weddle used to get interceptions like that?). Johnson has added four more interceptions through the first nine games of this season, a number bested by only two players (Charles Woodson and Mike Adams).
Speaking of Weddle, it is his pending departure as an unrestricted free agent that creates the need for Johnson in San Diego. Weddle's agent, David Canter, has said Weddle will not re-sign with the Chargers after Telesco failed to offer him a long-term contract extension in the offseason. The Chargers will likely seek a veteran to replace The Beard while using the draft to add a strong safety to compete with Jahleel Addae and Jimmy Wilson.
Johnson is the only NFL player to intercept two or more passes in a game in each of the last three seasons. Adding those playmaking skills to a secondary that already includes future All Pro Jason Verrett would give the Chargers something to build around on the back end of their defense.
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Michael Lombardo has covered the San Diego Chargers since 2003. He spent 12 years covering the team for Scout.com and has also been published by the NFL Network, Fox Sports, Footballinsiders.com and MySpace Sports. You can see more of his updates by following him on twitter @NFLinsider_Mike.