Thus, Casteel's enthusiasm for the nine regular starters who return to Morgantown this season is somewhat tempered by the loss of what he called "the quarterback of the front of the defense."
"You've got to have a kid that understands what he's doing and has leadership qualities," he said. "I think we have kids that can do that. But they're now going to have to accept that role."
"It's been easy with a guy like Reed Williams there, because he always had that role and embraced it. So we'll have to have a Pat Lazear, an Anthony Leonard or a J.T. Thomas step up and be able to take control. We had Grant Wiley, and that was tough when he left. But another guy fills in, and we'll find him. Hopefully we'll have two or three of them, and not just one."
If the defensive coordinator (beginning his 10th season in Morgantown as a Mountaineer assistant coach) can do that, he might be able to put together one of the stronger units at the school in recent years.
Defensive linemen Chris Neild, Scooter Berry and Julian Miller all are back to anchor the front of the odd-stack defense. The back end sees safeties Sidney Glover and Robert Sands (who was making quick progress towards the end of the 2009 season) back.
Casteel said he expected the knowledge that comes only with a season's worth of experience to benefit both of the rising sophomore corners as they try to work their way into the rotation.
"I think Lock [cornerbacks coach David Lockwood] is going to give those guys a lot of reps, and see where they come in," said Casteel.
"It's tough on a young kid to come in and learn a new system and what we call things. Even though it's pretty much the same, the terminology is different. So those guys have had a season under their belts and they'll get an opportunity to come in and have an idea of what we're talking about when we call a front or a coverage, and not just have to rely on being an athlete. So we're anxious to see how their growth continues."
While he admitted it's most always preferable to have players return that have experience, Casteel said true progression in the quality of play for the defense won't come unless each player makes improvements -- both in the weight room and in their knowledge of what to do within the the framework of the defense.
In that way, he said it shouldn't be assumed that returning starters automatically will earn their spots at the top of the depth chart once again this season.
"A lot of them put on a little bit of weight and get stronger than they were in the fall, and a little quicker," Casteel said. "It's a great time. The only thing problem with spring is most people want to know what the depth chart is. You think it's coach talk, but there is no depth chart."
"We have to put 11 guys out there every day, but they're not necessarily [the best 11]. We're trying to find the best 11. Obviously kids like Chris Neild and some of those guys are going to be in that mix. But there's a lot of positions that are really unsettled. That's why we enjoy going out and getting those guys reps. Then, at the end of the spring, we try to do our best to evaluate and go from there when we get into camp."
"If our kids continue to grow, we'll be better. If we don't, if our kids become complacent and don't try to improve, we'll struggle. Just having guys back is always better than not having anybody back, but there's still a lot of work to be done with everyone."
When going through the typical post-season process of "self-scouting" (extensively watching film of his defense to see what weak spots opponents could potentially expose), Casteel said the key points that stuck out were the need for his team to avoid giving up big plays and to be more solid in their tackling technique.
"It's the same things we see every year," he said. "We gave up a lot of big plays that happened at critical times."
"The way you're going to be good, though, is if you can get off a block and tackle, by and large. And those are the things you've got to continue to do as a football team."
On the positive side, Casteel said his team was solid on third downs and fared well in man coverage situations.
That latter note might be of particular interest, as being strong in man coverage can free a coordinator to call more aggressive blitz packages, which could, in theory, help put a stop to some of the big plays.
But Casteel was quick to say he didn't think that the lack of a consistent pass rush was the lone reason for opponents' long strikes.
"There's always a reason for everything," he said. "There are mistakes that happen within the defense, and from our standpoint, they obviously happen too many times. That's been uncharacteristic of us the last five, six, seven years. I don't think you can put just one reason why it happens. It's a combination of things."
For that reason, much as it is every spring, the focus will be on getting even experienced players better at the fundamentals of football.
"It isn't about scheme," said the veteran defensive coordinator. "They have 11 and we have 11 on our defense, so it's basically being able to do the fundamentals. Those are the things we have to emphasize to our kids really throughout the spring."