Northwestern's defense had its ups and downs in 2009. They struggled mightily in games against Syracuse and Minnesota early in the season, but played a huge role in their victories over Miami-Ohio and Iowa.
Even within a given game they were often inconsistent, following up a great half with a weak one (Penn State, MSU and Illinois) or vice versa (Purdue and Indiana).
When you add it all up, they finished in the middle of the pack in the Big Ten defensively, ranking sixth in scoring defense and fifth in total defense.
However, they were able to make some big plays on defense, ranking second in the Big Ten with 30 takeaways.
So what will the defense look like in 2010?
NU has to replace some key players, but several potential playmakers also return.
The defensive line looks like a mixed bag right now. The Cats lose starters Corey Wootton and Adam Hahn as well as tackle Marshall Thomas, but also bring back starters Vince Browne and Corbin Bryant.
Wootton was their most talented lineman last year, but he wasn't as productive as he was in his stellar 2008 season.
Corey was still working his way back to 100 percent most of the year after tearing up his knee in the Alamo Bowl. He finished with only four sacks and six tackles for loss, a down year for him.
However, he drew a lot of attention from opposing blockers. Without him drawing those blockers, the other defensive players could have a harder time making plays.
Quentin Williams and Kevin Watt will likely battle to replace Wootton in the starting lineup. Both have extremely limited game experience.
Also, neither one has the NFL-caliber combination of size and quickness that Wootton does, so there is likely to be a dropoff at this position.
On the other side of the line, Browne had a fairly solid sophomore campaign, especially considering he suffered a knee injury himself in 2008. Browne tallied five sacks and eight tackles for loss. He is a potential breakout performer thanks to his size and athleticism.
Bryant will return at one of the tackle spots, where he recorded 2.5 sacks and 5.5 tackles for loss. Vince Mafuli and Jack DiNardo saw some playing time as backup tackles, so they will likely be the contenders for the other spot.
Will any of the incoming freshmen be able to make an impact at this position? I doubt it. John Froland and Chance Carter are their two most highly regarded commitments so far, but both will need to build up their strength to make an impact at the college level.
It appears that someone will need to take a solid step forward for this to be considered a strong unit.
This should be the strongest unit on the defense. All three of the end of season starters return, as well as Ben Johnson, who started several games early in the year.
Quentin Davie was one of the biggest playmakers on the defense and will return at outside linebacker. He made plays all over the field, leading the team in tackles (90), tackles for loss (11.5), tying for the team lead in sacks (5) and forcing four fumbles. The junior linebacker could be an All-Big Ten contender.
Nate Williams will return to the middle linebacker spot. Nate tied for second on the team with 86 tackles while racking up seven tackles for loss and two interceptions. He was a steady player in the middle of the defense.
David Arnold rounds out an athletic group of linebackers. The converted defensive back only played in nine games but still managed to get two sacks and 4.5 tackles for loss as well as a forced fumble. With more experience, he could become a difference maker.
The previously mentioned Johnson and sophomore David Nwabuisi will probably be the main backups. Neither player seems likely to crack the starting lineup given the talent level in front of them on the depth chart.
The Cats will likely face some growing pains in the secondary. Departing seniors Sherrick McManis and Brad Phillips were both All-Conference selections, and Brad Smith was also a solid player when he was healthy.
NU will bring back two players with starting experience in Jordan Maybin and Brian Peters. Both players have significant talent but need to play at a higher level.
Maybin has the athleticism to stick with most receivers ,but it seemed like he always made a play after the catch was already made rather than when the ball was in the air.
He had two interceptions, but also didn't break up any passes and had an unusually high 75 tackles. If he can improve his ball skills, he could be a very solid corner.
As for Peters, he made some big plays (three picks, two forced fumbles, three fumble recoveries and 67 tackles even with a lot of backup duty) but also appeared to be out of position on several of the bigger pass plays that NU allowed late in the season.
While this is expected from a first-time starter, he's going to have to be more dependable in pass coverage this season.
They especially need to step up given that they won't have solid, veteran players at the other secondary spots like they did this season.
Justan Vaughn will probably be the leading contender to take over at cornerback. Vaughn was expected to play a major role in the secondary each of the last two years but had injury issues.
Demetrius Dugar and Ricky Weina also saw some time at corner and will likely see time in nickel and dime packages.
The other safety spot should be wide open. Hunter Bates and Jared Carpenter were listed as backups on the depth chart, but that could change during the offseason.
This is definitely a spot where freshmen could potentially make a difference. Ibraheim Campbell, CJ Bryant and Tony Jones all have solid athleticism and could conceivably steal a spot on the depth chart.
There are some talented players returning to Evanston next year, but the Cats also have some large holes to fill.
How well can they replace their departing starters? I'm not entirely sure.
The defensive line will probably be a key unit for this team. Their potentially suspect secondary could use a solid pass rush to make their jobs a bit easier and the linebackers are capable of making plays if the linemen can keep the blockers off of them.
I wouldn't be surprised if NU blitzed more frequently next year to try to force bad throws. If they try to rush four on a consistent basis, that puts a lot of pressure on both their new linemen and defensive backs to play at a high level.
If players like Browne, Maybin and Peters take the next step and they adequately replace one or more of their departing starters, this could be a solid unit given the overall athleticism. If they don't, their defensive inconsistencies will likely continue.