Why 2015 Is a Year of Defensive Dominance in College Basketball

In sports, we're always looking for trends. Sometimes we're just looking for trends for certain teams, players or segments of a game -- but, sometimes we look at trends on a much larger scale.

We often search for trends from year to year -- for example, the type of trend we've seen in the NFL and how it's really transformed into a passing game. For that type of trend we look at a lot of data, like how many pass plays, passing yards and passing touchdowns the 32 teams, as a whole, average over the course of the season.

Large increases or decreases in numbers like these often point to a particular reason.

As for the NFL, a lot of this comes from rule changes, including the amount of contact allowed in the secondary before a flag can be thrown. This is true for a lot of sports. Whether we like it or not, rules change.

Today, in college basketball, we're starting to hear a lot of chatter about making a change to the shot clock. In fact, in a recent ESPN poll, nearly 60% of coaches would welcome a 30-second shot clock. Many people see this as a way of speeding up pace of play and forcing an uptick in scoring.

On the other hand, just a week ago, my fellow contributor, Matt Goodwin explored the subject and came out with some contradictory findings.

Points per game hasn't really changed much since 2005. According to Matt's research, scoring has dropped just 1.85 points per game over the last ten years -- from 68.6 in 2005 to 66.75 in 2015.

However, scoring has dropped considerably this season. From last year to this year, we've seen a decrease of 3.3 points per game -- from 70.05 to 66.75 points per game. This is the biggest drop in the last 10 years, by a large margin, and is the most significant decrease we've seen since scoring dropped from 68.8 in 2008 to 67.3 in 2009.

So what happened in just one year?

Well, it could be a combination of things, but one thing is certain: there are a lot of good defensive teams in 2015. In particular, there are a handful of elite defensive teams like we've never seen before.

2005 to 2014

Below is a chart of elite defensive teams over the past 10 years. To be considered an elite defensive team, a team had to meet the following requirements: a nERD of 14.00 and an Adjusted Defensive Rating (according to kenpom.com) of 88.5 points per 100 possessions or better.

If you're new to the site, nERD may be new to you as well. nERD is our in-house metric that measures a team's overall efficiency and estimates a team's score differential against a league-average team on a neutral court.

Which teams meet that criteria?

One easy takeaway from this chart is that every year is different. In 2006, three teams met the criteria but none of them had an Adjusted Defensive Rating better than 88.1. In 2013, four teams met the criteria and three had an Adjusted Defensive Rating lower than 88.0 points per 100 possessions. Then, just a year ago only one team made the cut -- and just at the threshold point at that.

Here's seven other takeaways:

1. There were two years (2005 and 2011) in which no teams met the criteria, and two years -- 2008 and 2013 -- in which four teams met the criteria.
2. The 2008 Wisconsin and 2013 Florida teams gave up the fewest points per game to their opponents.
3. Kansas' 2008 national championship team, on the back of Mario Chalmers' huge three, had the best season in terms of nERD and win percentage.
4. The 2009 Memphis Tigers posted the single best Adjusted Defensive Rating.
5. In addition to two national champs, three national runner-ups also help make up the field.
6. Every team had at least a win percentage of 75% or better.
7. Last year's Arizona squad, tied UCLA for the worst Adjusted Defensive Rating among the eligible teams.

2015

Arizona's 2014 team led the entire nation with their Adjusted Defensive Rating of 88.5 (the minimum requirement). This year is an entirely different story.

Here's five teams so far in 2015 that possess a better rating.

This is the first year in the last 10 years in which five teams meet the requirement for our elite defenses in college basketball. Accordingly, this year's top defenses trump those of 2008 and 2013.

Even with Lousiville's baseline nERD of 14.00, these five teams have an average nERD of 18.34, which is better than all but five teams that met the criteria over the past 10 years. Kentucky possesses the best team nERD and win percentage among all eligible teams, and they might just be the best college basketball team we've seen this century.

Both Virginia and Kentucky surpass Memphis' best Adjusted Defensive Rating and are the only two teams with ratings below 85 points allowed per 100 possessions -- Virginia being the only team under 84 points per 100 possessions. The defensive juggernauts are also one and two among all eligible teams in opponents points per game and win percentage.

But, there are also three other strong defensive teams right behind the Cats and Hoos. Arizona, Utah, and Louisville all have win percentages of at least 78.6%, while none of them give up even 59 points per game or have an Adjusted Defensive Rating worse than 88.3.

It's not a shocker then that, according to our power rankings, Kentucky, Virginia, and Arizona are three of the four best teams in the country. Meanwhile, all five teams are firmly in the NCAA Tournament, and our numbers project each of them to earn a 4 seed at the very worst come March Madness.

Keep an eye on these teams as tournament time nears. They should all be big factors in how this year's tournament plays out, and I'd look for at least three of them to make the Elite Eight and compete for a national championship, like good yet inferior defensive groups have done in recent years.

The old cliché -- "Defense wins championships" -- might just play out this year when all is said and done.