Northwestern's Offensive and Defensive Effectiveness

Raise your hand if you predicted Northwestern's season to go at all like it has up to this point. If your hand is up, you're lying. Before this season started, I did not expect much from this team. Few did. Aside from Crawford and Cobb, the team appeared to lack talent. Through the non-conference schedule and early conference schedule, the 'Cats seemed to be affirming my predictions. Well, actually, they seemed even worse than I predicted. I all but threw this season out and was actually starting to worry about Collins as a coach. Then, all of a sudden, something clicked. Northwestern didn't look any prettier on the court, but they started winning. And these are not cupcakes they've been beating. They're 5-2 in their last 7 with wins over Illinois, Indiana, Purdue, Wisconsin, and Minnesota. ...Wow. Collins and the 'Cats made me look like a fool, and I love it.
Now let me make something clear right up front: Northwestern's recent degree of success is an anomaly. This is not to say it's been unearned, but, statistically speaking, it makes very little sense. According to Ken Pomeroy's predictive ratings (which are usually very, very good), we should be the 109th best team in the country and worst in the conference. Statsheet.com suggests that, statistically speaking, we are 93rd in the country and 10th in the conference. According to Sports-Reference's Simple Rating System we're the 97th best team in the country and last in the Big Ten. Despite all this, the 'Cats are sitting at 5-5 in conference, good for a tie at 4th place. Let's take a look at some stats and see if we can make heads or tails of this success.

Offense

Looking at points per game, Northwestern's offense looks truly awful, scoring only 61.3 points per game. This means they are tied for 342nd in the country (out of only 351 teams!) and dead last among teams in BCS conferences. Limiting the search to only conference games, the period during which NU seems to have hit their stride, does not help. Here, the Wildcats are only putting up 54.3 points per game. Only one team, Washington State, has a worse mark in the country.
"Ok," you may be saying to yourself, "using points per game as a scale of Northwestern's offense is not fair." You would, of course, be exactly right. Northwestern plays at an extremely slow pace (according to KenPom.com, only 10 teams play slower). As such, they get off fewer shots than other teams, and, consequently, will score fewer points. So let's take a look at some tempo-free statistics. According to Ken Pomeroy's adjusted offensive ratings, the 'Cats are scoring only 95.8 points per 100 possessions, good for 314th nationally. This is a slight, but only very slight, improvement over the ppg rating. To put this number into context, last year's terrible Northwestern team had an AdjO of 101.8 ( 151st in the country), and the uncharacteristically good 2012 team had an excellent AdjO of 113.3 (16th in the country).
So, Northwestern's offense has not been good. But why? Reason one is simply that the Wildcats are shooting poorly. They have a true shooting percentage (a measure that appropriately weights the value of 2-pointers, 3-pointers, and free throws) of 50.2%. That's 320th in the country. This poor shooting is very visible behind the arc. In a number that would surely make Bill Carmody cry, NU is only making 30.2% of their threes. That number drops to 26.5% in conference games.
Considering Northwestern has many of the same players as were around in the Carmody era, why is there such a significant drop off? The answer primarily lies in the change of system. In Collins's new pick and roll system, players are getting fewer open looks, leading to a drop in percentages. The Wildcats's current players simply are having difficulty creating their own looks (with the exception of Demps and occasionally Crawford). The change of system becomes very clear when looking at assist numbers. Whereas the wildcats were consistently among the best nationally in assists per game under Carmody, they are 265th nationally this year. Of course, considering NU's low scoring, a fairly large percentage of NU's points still come off assists, but, given that the Wildcats were top 5 in assist percentage in every year of Carmody's tenure, their decline is still a very large drop-off.
One final issue with Northwestern's offense lies in rebounding. While the Wildcats have not been good at offensive rebounding at any point in recent history, their paltry 7.9 per game stand out as even worse when coupled with the 'Cats poor shooting.

Defense

So it's clear the Northwestern offense is not good. So is the defense better? Yes, and it's not even remotely close. In terms of of PPG allowed, Northwestern is 32nd in the country and 2nd in the conference, allowing only 63.3 PPG. Looking only at conference games, the Wildcats are still at 63.3 PPG, but, here, that's best in the conference. 

Now, of course, in the same way a slow tempo can hurt offensive numbers, it can also help defensive numbers. So it stands to reason the Wildcats' adjusted tempo-free numbers would take a hit, right? Actually, the answer is no. According to KenPom's AdjD, the 'Cats are allowing only 91.6 points per possession adjusted. That's 11th in the country! 

Of course, if you've been following the Wildcats for the last several years, this seems insane. Even when Northwestern has been a good team, the defense has been sneaky-good at best and beyond atrocious at worst. So how are the 'Cats playing legitimately solid defense? For one thing, they're just not letting teams get good looks. Their 49.1% TS% allowed is 31st in the country and best in the conference. Typically, when teams have good defense in regards to TS%, it comes, at least in part, due to the team not allowing their opponent to the rim. However, Northwestern has allowed a fairly high 38.6% of opponents shots to occur at the rim. Despite this, they are allowing only 56.1% of those types of shots to fall, good for 4th in the Big Ten. The Wildcats are at there best when they slow down there opponents in the half court game and funnel driving players into Alex Olah, and they have been doing this successfully. 

Also adding to the Wildcats' success is that they have been grabbing defensive rebounds at a much higher rater than previous years. Their 26.3 defensive rebounds per game is good for 43rd in the country and puts their 21.8 from last year and 20.8 from the year before to shame. 

Overall

So, long story short, Northwestern has had a dreadful offense and a fantastic defense. In fact, according to Ken Pomeroy's ratings, nobody else has as large a disparity between offensive and defensive efficiency as do the 'Cats. Fortunately, as of late, Northwestern has been able to play its strengths, acknowledging that they won't be able to put up many points and just making sure their opponents put up even fewer. However, it should be noted that what they have been doing may not be sustainable. According to Ken Pomeroy, the 'Cats are one of the luckier teams in the country. Of course, "luck" here does not necessarily refer to luck as we typically think of it. It's simply a measure of the disparity between expected and actual outcomes. Factors, other than actual luck (such as late-game coaching) may come into play. Hopefully Northwestern can keep up its magical run, but, to be honest, it will be far from easy.