Coming into this season, there seemed to be little reason to believe that Northwestern's porous defense from last year would be any better this year, especially with the graduation of some of that unit's best playmakers: safety Brian Peters, cornerback Jordan Mabin, linebacker Bryce McNaul, and linemen Jack Dinardo and Vince Browne.
But whether it was new talent coming in, improvements from the returnees, fresh leadership, or some combination of the three, NU's defense stepped up by leaps and bounds in almost every single measurable. It was the difference between last year's 6-7 team and this year's 9-3 squad.
NU's points yielded dropped by nearly 5 points a game, from 27.7 last season to 22.8 this year. Rushing yards against per game decreased by almost 50 ypg, from 177.3 to 122.8, ranking third in the Big Ten. Passing yardage increased against the Wildcats, largely due to more opponents having to play from behind against NU (the Wildcats faced the most pass attempts in the Big Ten), but yards per attempt dropped from 8.4 last year to 6.7 this year, a huge improvement.
Turnovers forced increased from 20 to 25, and turnover margin went from +3 to +13. Opponents' third-down conversion rate went from 50% last year to 43% this year. Sacks increased from 17 to 25, and while interceptions were down, pass break-ups went from 30 last year to, get this, 60.
Probably the most telling stat is this-- in 2011, the top two tacklers for NU were both safeties in Ibraheim Campbell and Brian Peters, who combined for 192 tackles. In 2012 so far, NU's primary two safeties, Campbell and Jared Carpenter, are fourth and fifth on the tackle list, combining for 141 tackles. You don't have to be a genius to know that having your safeties lead your team in tackles is generally a bad thing.
The improvement in the defense started up front, with the line combining for 32 tackles for loss, including 17.5 sacks, up from 23.5 TFL and 11.5 sacks last year. Tyler Scott led the way with 9.5 TFLs and 7 sacks.
At linebacker, the starting combination of Damien Proby, David Nwabuisi and Chi Chi Ariguzo was as solid a unit as I can remember for a long time. Nwabuisi and Proby were starters last year, too, and they made major strides this year, while Ariguzo was a first-time starter and is only a sophomore.
In the secondary, Ibraheim Campbell built off his successful freshman year with a solid second campaign, and Nick Van Hoose was a revelation at one of the corner spots. Jared Carpenter got better as the season progressed, I felt, and while the combination of Daniel Jones, Quinn Evans and Demetrius Dugar struggled at times, each of them made some big plays down the stretch, and the unit as a whole performed a lot better than last year's secondary.
All of this was achieved with basically the same exact defensive scheme that NU has had since defensive coordinator Mike Hankwitz came on board. NU essentially runs a straight-up 4-3, cover-4 defense, with the outside corners giving some cushion to the receivers to protect against the long bomb. Occasionally, Hankwitz will show a nickel defense that involves three rushers, and occasionally, he'll blitz. But the basic bend-don't-break scheme is the same.
All of which is to say, credit is due to everybody involved with the defense's improvement: the newcomers for injecting some life into the unit, the veterans for upping their games, and the coaches for developing the players and making the right calls. Northwestern still isn't exactly a world-beater on defense, ranking near or at the bottom of the Big Ten in some statistical categories, but on the whole, there's no doubt about it: the defense is most responsible for the program's resurgence this year.