Philadelphia, PA (Sports Network) - It has been a few years since Notre Dame factored into the BCS, with only two double-digit win totals since Lou Holtz led the Fighting Irish to an 11-1 record and a second-place finish in 1993.

Tyrone Willingham led Notre Dame to a 10-3 record in his first season in 2002, but the team finished the season just 17th nationally. Charlie Weis posted the same 10-3 mark in 2006, also resulting in a final ranking of 17 in the Top 25.

Einstein's famous formula of E = MC2 is mirrored in the 2012 Notre Dame football program, specifically on the defensive side of the football, and it is a formula that coach Brian Kelly has adopted thanks in large part to the scheme of defensive coordinator Bob Diaco, whose 3-4 no-crease defensive front is paying huge dividends in 2012, making Notre Dame relevant again.

The left side of the equation comes from the energy level that is displayed throughout the Irish defense. It is an energy that reverberates throughout the entire team and, for that matter, a fan base desperate to relive the glory days of old.

The right side of the equation is what causes the elevated energy level and that is a defense that is bigger and faster than in years past, one that has matured into a group that is now taking the fight to opposing offenses instead of just surviving the day.

It starts up front, with a line that features a pair of 300-pounders at the end positions in senior Kapron Lewis-Moore (6-foot-4, 306) and sophomore Stephon Tuitt (6-6, 303), and monster nose guard Louis Nix III (6-3, 326). Tuitt has thrived in his pursuit of opposing quarterbacks this season, recording a team-high six sacks in the first four games.

Behind the oversized defensive line is a quartet of big linebackers, headlined by Notre Dame's defensive jewel in two-time All-American Manti T'eo in the middle. The 6-foot-2, 255-pounder is regarded as perhaps the very best linebacker in the country and has certainly played like it in 2012, leading Notre Dame in tackles (38), while recording three interceptions and two fumble recoveries.

A complete package at linebacker, T'eo has size, speed, football acumen and killer instincts. The remainder of the starting linebacking corps consists of juniors Prince Shembo (6-2, 250) and Danny Spond (6-2, 248), and senior Dan Fox (6-3, 240).

The Irish secondary is the least experienced group, but anchored by senior safety Zeke Motta (25 tackles). Junior cornerback Bennett Jackson (22 tackles, three interceptions) also has made his presence felt in the first four games.

The defense has recorded 14 sacks and 13 takeaways and it's not like Notre Dame has racked up the big plays against suspect competition.

After blasting Navy in the season opener in Ireland (50-10), the Irish have beaten a trio of Big Ten teams, slipping by Purdue (20-17) before handling Top 20 foes Michigan State (20-3) and Michigan (13-6) with relative ease, defensively speaking.

The Spartans' prolific rushing attack was held to a mere 50 yards on 25 carries, with star tailback Le'Veon Bell getting shut down to the tune of just 77 yards. The Irish followed that by limiting Michigan's Denard Robinson to just 90 rushing yards and 138 passing yards, and kept him out of the end zone. Talk about big plays - Notre Dame recorded its five interceptions on five straight Michigan pass plays.

It's the big plays on defense that have defined Notre Dame's season to date.

"Well, I think it's always been predicated about keeping the points down, and we've seen that there's been that increase each and every year," Kelly said. "We're keeping the points down, and we're also now taking the football away. I think we're close to as many turnovers as we had last year after Week 4. The combination of keeping the points down and not having, OK, you're a-bend-but- don't-break defense, now we're a stingy defense and we're a defense that can take the football away. That's the next level of championship defense."

The Irish will enjoy a well-deserved bye this week before embarking on an ambitious October and November. On the docket the rest of the way are high profile games against Miami (Fla.), Stanford and Brigham Young at home, and Oklahoma and USC on the road.

If Notre Dame's defense stays consistent and actually improves the rest of the way - as hard as that is to envision - then the winning formula in South Bend is likely to be D = BCS.

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