Free-agency review: Chargers

Most significant signing: Re-signing linebacker Donald Butler as the long-term anchor for the middle of San Diego’s defense was the team’s top priority in free agency, so mission accomplished. The University of Washington product has had trouble consistently staying on the field. But with his athleticism and playmaking ability, Butler has the potential to blossom into a perennial Pro Bowl player.

Most significant loss: It might not be felt on the field, but Charlie Whitehurst leaving the Chargers in free agency to join former San Diego offensive coordinator Ken Whisenhunt in Tennessee will be felt in the quarterback room. Whitehurst is a close friend of Philip Rivers, and served as a good sounding board for the franchise quarterback in practice and in games.

Biggest surprise: Some league observers raised eyebrows over the Chargers signing Indianapolis Colts free-agent running back Donald Brown to a three-year, $10.5 million contract, including $4 million in guaranteed money. Critics of the deal surmised San Diego had enough depth at running back with Ryan Mathews and Danny Woodhead, and that money could have been better spent on more obvious needs such as cornerback or outside linebacker. However, the Chargers have morphed into an offense that leans on the running game. So if Mathews is banged up, San Diego needs a running back with a similar skill set to effectively run in between the tackles. Add to that the fact that Mathews and Woodhead are free agents at the end of 2014, and Brown offers some insurance in case either player does not return.

What’s next? As the second wave of free agency approaches, the Chargers still have holes to fill at cornerback, defensive tackle, interior offensive line and receiver. Players who could make some sense for San Diego include Denver Broncos free-agent cornerback Champ Bailey and, if released, New England Patriots defensive tackle Vince Wilfork.