Nowhere on the 2011 Notre Dame team has the phrase "next man in" come into play more than along the defensive line.
No fewer than 13 players have aligned with a hand on the ground through the first nine games of the '11 season, and the Irish have needed every one of them, particularly once veterans Ethan Johnson and Kapron Lewis-Moore went down with significant injuries in the Purdue (Johnson) and USC (Lewis-Moore) games.
"It was No. 1," said Brian Kelly, referring to the defensive line depth and where it ranked on his priority list when he began assembling what has become a rather stout defense. "It started with the defensive line."
Since the dark days of the 2009 season and even extending into the first eight games of the Kelly regime, the Irish have shaved off 36.2 yards rushing and 69 yards passing per game by the opponents. That's a 105-yard decrease in yards allowed per game in the last 13 compared to the previous 20.
It starts up front with veterans Johnson and Lewis Moore. It continues at nose guard where Sean Cwynar has provided yeoman-like work and Louis Nix III has emerged as a force. It carries through with players such as Darius Fleming, Prince Shembo, Ishaq Williams and Steve Filer - outside linebackers who have lined up in a three-point stance - and continues with backups such as Chase Hounshell and Hafis Williams.
It also prominently includes two other freshmen, Aaron Lynch and Stephon Tuitt, who were Godsends as backups, and even more valuable now that they've had to step into the starting lineup in the absence of Johnson and Lewis-Moore.
Lynch and Tuitt were outstanding in helping the Irish pitch a second-half shutout at Wake Forest last Saturday night.
"That's why you take four flights and you wait in the airport for a flight into South Bend that's been canceled six times," said Kelly, speaking of the extreme measures the Irish coaching staff went to in order to land Lynch and Tuitt.
"That's the work that our guys have put in because we knew the importance of putting our football program in the position we need moving forward (by) developing that depth on the defensive line. That was job one."
But that's just the first step, according to Kelly. There's work to be done as the Irish work their way to the back portion of the defensive unit.
"We're not done," Kelly said. "Our second phase is what we're into recruiting right now, and that's the secondary. You look at Wake Forest for example. That was a deep and talented group of young men, not that we don't have players. We do. But we're nowhere near Wake Forest in terms of depth on the back end of our defense.
"So that will be the next point of emphasis in terms of developing our defensive backfield. That's the next stage of developing a great defense. You start up front (and) control the line of scrimmage."
Of course, the Irish will have to evolve with the adjustments of the opposition, which will quickly learn over the long haul that trying to run the football against Notre Dame is like beating your head against a wall.
"The next challenge that teams aren't going to run the ball against us," Kelly said. "They're going to see that (they) need to get the ball out on the perimeter and (they) need to challenge (our) secondary, and that's where we have to continue to build on the defensive side of the ball."
One step at a time, brick by brick, starting with the foundation - the defensive line.