You are likely to see Castillo firing up and down the Eagles sideline at Lincoln Financial Field on Thursday night, urging intensity and execution from his defense. It isn't an easy balance, either, with only 20 seconds of time to make the call for the next snap of the football and send it in to his defensive signal caller.
How does Castillo manage to get so much in -- the reaction to the play, the call of the next snap -- in so little time?
For all of the excitement of seeing Michael Vick and the Eagles offense take the field for the first time in the preseason, the defense deserves its large slice of the spotlight, too. There are so many new faces here starting at the top: Castillo has never coached a defense in his NFL career.
"I'm like everybody else here," he says. "I learn every day. You learn every day in your job. I know that I'm going to keep doing that for the rest of my life. The key for me is to keep working hard and keep getting better. That's what I'm going to do.
"I know that these players have given me all of their attention. They are ready to play some football."
The Eagles haven't done any tackling in training camp, preferring instead to emphasize technique and progress slowly from there. There has been plenty of contact in this high-speed camp, but not once has a defensive period been "live," as has been the case in every one of head coach Andy Reid's previous camps here.
In fact, Reid has historically run one of the more physical camps in the NFL. But with no offseason to teach technique, Reid and the coaches decided to bring everyone up to speed at the same time, patient step by patient step.
Two and a half weeks later, a game is upon us.
And the Eagles defense gets to see a physical, brawling Ravens offense that is likely to try to pound the football.
"I'm sure we're going to see a lot," said defensive tackle Cullen Jenkins, one of the many new faces on the defense. "That's what the preseason is for. You shake off the rust and you get up to speed for the regular season. It's football. It's what we love to do."
Castillo's defense has played well in training camp. The upgrade in speed and talent is obvious to everyone. How he uses his personnel, how many blitzes he dials up, what call he makes on a critical third-and-2 snap is what everyone is looking to see.
What you see on Thursday isn't necessarily what you are going to see when September 11 rolls around. This is just a dip into the ocean. Castillo has a lot of ideas for a defense that has as much depth up front as any Eagles team ever has, and as much coverage ability as any defense here has ever enjoyed. He isn't going to show his hand here.
But there are some important phases to this game for the defense. How does the front seven handle the power running game? Is rookie Casey Matthews going to take a step forward as the starting middle linebacker? Where are all the plays coming from at the linebacker spots? How many times will Nnamdi Asomugha, Asante Samuel and Dominique Rodgers-Cromartie be on the field at the same time?
The starters will play for a quarter and then the coaches will turn it over to the reserves. Important roster positions are up for grabs. How these players grasp Castillo's scheme is critical after just a couple of weeks of learning. Finding out how the young players and the veteran newcomers react to playing against a different team is what the preseason is all about.
I can't remember being as excited for a preseason opener as I am for this one. Oh, I know the only thing that really matters is that the Eagles emerge with minimal bumps and bruises, but given the unusual circumstances of the offseason, this game is more than just an opener. It is a beginning of the sense of discovery for an Eagles team that has undergone massive changes since the 2010 campaign ended on an intercepted pass in the end zone.
The defense has had the most change, so naturally the curiosity factor is highest here. The players are one thing, for sure. Everyone is amped to see the new guys. But the one man who matters most is Castillo, who takes his work ethic and his love for the game to the other side of the ball, to a defense that needed -- and received -- a massive transfusion of change.