He has played well and improved over his relatively short career, and the Chargers recognized that and gave him a large contract extension last year.
However, he finds himself entering an offseason where even his spot isn't safe.
Defensive rotations during OTAs have been very fluid so far. Antonio Garay, Jacques Cesaire, and Ian Scott have all shared time with Castillo during drills so far.
While this interesting change may not mean a whole lot, it sure follows along with GM AJ Smith's "new plan".
Smith is holding everyone accountable this offseason. He is threatening to cut the salaries of RFAs Vincent Jackson and Marcus McNeil, and he has brought in players through draft and free agency to create stiff competition at every position on the field.
There is a lot of hype surrounding other backups on the field, from Jyles Tucker to Mike Tolbert to Malcolm Floyd, and all of this suggests a feeling within the Chargers that they are willing to move on and rely on their taxi squad.
Ultimately, I expect Luis Castillo to stick to the first line DE spot. The other positions, from the D-Line to Linebacker to D-Back, are all fluid.
Just for fun, then, here's a projection of what the roster might look like at the end of the offseason
DE: Luis Castillo, Travis Johnson, Jacques Cesaire
DT: Cam Thomas, Vaughn Martin, Ian Scott
LB: Shawne Merriman, Shaun Phillips, Larry English, Jyles Tucker
ILB: Brandon Siler, Stephen Cooper, Kevin Burnett
CB: Antoine Cason, Quentin Jammer, Donald Strickland, Nate Vasher, Dante Hughes
S: Eric Weddle, Darrell Stuckey, Kevin Ellison
This will be a very interesting offseason. I expect the order of these names to change. A lot. Only time will tell what this team will look like come September.