Castillo played in 15 games last season, the highest total since 2005, yet recorded a career-low 1.5 sacks. His lack of production can be explained in part by a nagging back injury and in part by having no Shawne Merriman to draw attention from him.
Nonetheless, the team needs Castillo to return to his 2006 form, when he averaged 0.7 sacks per game (which projects to 11 sacks over a 16-game season).
The real questions reside at right defensive end, where the team has yet to make a move to replace Igor Olshansky, who started 70 games there over the last five years.
DE Jacques Cesaire (R)
Also in the mix is Ryon Bingham, who splits his time between defensive end and nose tackle. Bingham is extremely valuable because his versatility allows the team to keep just five defensive linemen active on game days. Bingham is a favorite of the coaching staff because he's made marked improvement in each of his five seasons. However, his versatility is best served as the fifth lineman in the rotation.
The Chargers have two youngsters looking to bring up the back end of the rotation. Keith Grennan was promoted from the practice squad to the active roster last season before promptly going down with a season-ending leg injury. He is a run-stopping lineman and is more efficient than flashy.
Also looking to stick is Andre Coleman, who's spent the last two seasons on the practice squad. Coleman has been compared favorably by his teammates to former Charger DeQuincy Scott because of his quickness as an interior pass rusher.
The Chargers will look to address this position via the draft. Ideally, the team can find a player who can be groomed to take over for Cesaire at right end. The Chargers could fill this need in the first round with LSU's Tyson Jackson or wait until the middle rounds for a player like Georgia Tech's Vance Walker or Stanford's Pannel Egboh.
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.