So Bowles has to find a way to maintain that steadiness while injecting a bit more intimidation, aggressiveness, and creativity.
To further muddy the waters, Bowles has never been in the role of defensive play-caller before. That was one of the huge gaps in Castillo's resumé, too. As a former NFL defensive back and career defensive coach, Bowles should be better prepared than the converted offensive line coach, but it is still a new area. He would have been much better served by having a preseason to work out the bugs.
It is too late for that. Bowles has to step right in and deliver against the undefeated Atlanta Falcons on Sunday. Eight days later, he has to take on Drew Brees and the still-dangerous Saints in New Orleans.
So what can Bowles do? The crowd-pleasing answer is simple. He can blitz Matt Ryan until the Falcons quarterback seeks career counseling. After watching three games with zero sacks, the home fans are starved for the kind of reckless, intimidating defense they consider their birthright.
But here is the tougher question: Whom does Bowles send?
As coach Andy Reid pointed out, Castillo was blitzing at times. The problem was, the players he sent didn't necessarily arrive. That tilted the risk/reward calculation sharply in favor of the offense.
Neither of the Eagles' starting safeties, Kurt Coleman and Nate Allen, has much history of blitzing successfully. Allen did have two quarterback sacks in 2010, when he played in just 13 games. Coleman has zero career sacks.
Other teams have had great success confounding Michael Vick with cornerback blitzes - a ploy Jim Johnson used effectively when he had Troy Vincent and Bobby Taylor - but look at the Eagles starters there. Nnamdi Asomugha and Dominique Rodgers-Cromartie are fine in coverage, but neither appears eager to initiate contact.
Asomugha has exactly two career sacks, the most recent in 2006. Rodgers-Cromartie has one. As for slot corner Brandon Boykin, he is worth a try. He doesn't exactly have the size to be an intimidator, though.
That leaves the linebackers. Weakside linebacker Akeem Jordan has one career sack, so he's probably not about to turn into Lawrence Taylor.
DeMeco Ryans? Now we're getting somewhere. The middle linebacker had 51/2 sacks in his first two seasons in Houston, but has had no more than one per season since. Still, Ryans has shown a knack for getting into the backfield and being disruptive.
"Whatever Todd calls, I'm all for," Ryans said Wednesday. "It's up to him and whatever he calls."
Maybe the most intriguing candidate is rookie linebacker Mychal Kendricks. He has handled the responsibility of starting at strong-side linebacker surprisingly well. But he did have 131/2 sacks during his college career at Cal. It may not be a bad idea to turn the kid loose every now and then, see whether he has that mean streak that defines great playmakers.
"That's my thing," Kendricks said, quickly adding that he didn't know whether it was on Bowles' to-do list.
"Right now," Kendricks said, "we're keeping everything basic, simple, basically doing the same stuff that we've been doing. You're going to have to ask him that because I'm not in his head. But as far as I'm concerned, I would love that."
So would the fans.
Bowles has other options. He could stand up Jason Babin or Trent Cole and have him rush as a linebacker with four other linemen in the formation. He could devise more creative blitzes that give otherwise unlikely players a clear path to the quarterback.
Johnson was a master of knowing whom to send and, just as important, when to send them. He also wasn't daunted when the occasional blitz backfired.
Bowles hasn't built that kind of equity, with either the fans or the players, just yet. He has to take some calculated risks, but he can't afford to get burned too badly. He has to make a mark on this defense, and he has no margin for error - not in Week 8, with his boss' job on the line.
Other than that, his new job should be a breeze.
Contact Phil Sheridan at firstname.lastname@example.org, or follow on Twitter @Sheridanscribe. Read his blog, "Philabuster," at www.philly.com/philabuster. Read his columns at www.philly.com/philsheridan