Hidden under the pile of rubble that was the Brady Hoke era was a team designed for Jim Harbaugh to take over and have immediate success. Inheriting five returning starters along the OL, the tight end of his dreams in Jake Butt, plenty of mobile bludgeons at fullback and H-back and some established weapons on the outside made things straightforward.

Evidently not one to count his eggs before they hatch, Harbaugh also added transfer QBs Jake Rudock (Iowa) and John O'Korn (Houston) while also securing another freshman, pushing the number of scholarship QBs on campus to six.

But where Harbaugh really struck gold was in the defensive talent he inherited. The Wolverines quietly ranked 18th in defensive S&P+ in 2014, returned about a dozen important contributors and retained DL guru Greg Mattison on the staff.

Harbaugh then made Nick Saban/Will Muschamp disciple D.J. Durkin the coordinator, and the former Florida DC has maximized the roster with a current ranking of fourth in defensive S&P+, allowing just 14 points since Week 1. Michigan has the chance to make some loud noise with a schedule that sees the Wolverines host both Michigan State and Ohio State.

Harbaugh's "manball" approach on offense makes great defense a priority, but also a more manageable task. Without a physical, demanding culture, it's hard to build a defense of players who work in tandem, sacrifice for each other by taking on blocks and intimidate opponents. And without a bevy of talent, defense becomes especially difficult, as it's less of a skills-based trade than offense.

When those two are in place, as they are in Michigan thanks to Harbaugh's oversight and Hoke's recruiting, good scheme can be brought to bear. Durkin's schemes are good enough that the Wolverines might end up having the league's best defense.

Winning up front

The greatest asset Michigan has is a loaded front that includes at least five big DL who could start at most other places around the country. Durkin follows the Muschamp school of fronts (which is really the Bill Belichick school) and emphasizes multiple techniques, multiple fronts and a focus on creating matchups for the DL.

Durkin has a nice man-blitz package that he uses liberally, but the fronts are designed to allow Michigan to put players like DE/LB hybrid (what Michigan calls the "buck") Mario Ojemudia in positions to create havoc.

Ojemudia is now out for the season with an injury, with lightly experienced senior Royce Jenkins-Stone next up at buck.

Because the Wolverines have several good defensive tackles, they can move them around and keep them fresh to collapse the pocket. When Michigan is facing a passing down or an opponent lined up with four receivers, it'll play a dime package that will include three of those tackles, the buck and senior LB Desmond Morgan.

The buck is moved all around to either become a DE or interior blitzer, while the other DL attack the offensive line and play through blocks. Because the DL are taught multiple techniques, they can move in favor of matchups.

If the opponent is in a three-receiver package, Michigan will match it by joining Morgan with another of its many good inside linebackers (usually senior Joe Bolden) while playing the buck or DE Taco Charlton as a stand-up end next to three DTs.

It's very difficult to move this off the line of scrimmage, because a typical front looks like:

At other times, Michigan will move Maurice Hurst (team leader in sacks, with three) to nose to shoot gaps, play Charlton on the edge and put big Chris Wormley (team leader in tackles for loss, with seven) in the 3/4-tech position.

With the buck inserted God-knows-where, one or two senior inside linebackers flowing to the football behind the tough DL and often an eight-man front with DBs forcing the edges, it's hard for opponents to find leverage up front, even against a dime package.

Holding up on the back end

Michigan's approach to pass coverage is similarly matchup-focused. Again, the Wolverines have a lot of players to work with that allow them to do different things to cause problems. They're relatively simple, playing mostly man coverage underneath, and that allows them to move players around.

Against BYU's surging passing game, the Wolverines deployed 6'4 DB Jeremy Clark on the Cougars' favorite big target, 6'6 Mitch Mathews, while playing the quicker, 5'10 Jourdan Lewis on BYU's shorter slot weapon, Mitchell Juergens.

Many offenses look to move their WRs around until they're in spots where the opposing team's coverage structures aren't well-equipped to handle.

Michigan doesn't really care where you put your best receivers. The Wolverines are going to line up in press-man coverage with two (or is it just one? or zero?) deep safeties over the top. Their DBs will follow their assignments, whether at field corner, boundary corner, nickel or wherever.

Here, Michigan has safety Jabrill Peppers outside, playing his primary high school position and pressing the field corner (bottom of the screen cap), Lewis on the slot, safety Delano Hill at linebacker to cover the TE and Clark at boundary corner (top of the screen cap).

Because the Wolverines have the speedy Lewis pressed up on a quick possession target and longer players pressed up on bigger targets, there are often no safe places for the QB to quickly deliver the ball. The other coverage players also play up tight, which has the same effect and buys time for the big DL to collapse the pocket.

Opposing teams that rely on beating zone coverage with timing are thrown off because their receivers are jammed at the line. Passing games that welcome man coverage and feast on matchups are also looking at a tough proposition against flexible DBs who can play multiple positions.

The only missing ingredient for the Wolverines is playmaking from the support players in the middle of the field. Safeties Delano Hill, Jarrod Wilson, and Peppers need to take advantage of their opportunities in zone coverage and make some picks. Michigan ranks No. 35 in interceptions per game so far, and that could improve.

They're doing a good job preventing big plays, but if they make that step, this defense will be an absolute nightmare.

Remaining challenges

Michigan has a very navigable schedule, with only two teams ranked in the top 50 in offensive S&P+ (which doesn't include Ohio State, who will surely end up there). Only one of those, Indiana, is on the road.

The other challenge will come when Michigan State brings a smart offensive attack and potentially punishing run game into town and looks for ways to gash the Wolverines with big runs or Connor Cook threading the needle against man coverage. If Michigan's D can see it through that game, it should set up for an exciting conclusion against Ohio State in Ann Arbor with a lot at stake.