What are the NET rankings in men’s basketball?

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In the 2018-19 men’s basketball season, the NCAA started leaning on something called NET rankings when comparing team resumes come tournament time. But what are NET rankings, and how do they work?

The N.E.T., or “NCAA Evaluation Tool” Ranking, is a system used by the NCAA to rank men’s college basketball teams, both during the season and when it comes time to select and seed tournament teams. In 2018, it replaced the RPI, which had been around since 1981 but had become increasingly disfavored over time.

According to the NCAA general description of the system, the NET evaluates a team based on “game results, strength of schedule, game location, scoring margin, net offensive and defensive efficiency, and the quality of wins and losses.”

Okay, fine. We’re going to look at stuff that matters when trying to figure out how good a team is. Good start.

A more detailed explanation identifies five main factors in the NET Ranking: Team Value Index, Net Efficiency, Winning Percentage, Adjusted Win Percentage, and Scoring Margin.

Team Value Index

The Team Value Index component of the NET is a results-oriented algorithm designed to reward teams for beating other good teams. The man remains mysterious behind the curtain, but the NCAA has said that this component includes factors such as who won (duh), the opponent (okay, good), and the location (um, okay.) I’d love to see more detail on what’s happening inside the machine here, but I doubt they’re going to make the process that transparent.

Net Efficiency

The second component is Net Efficiency, which is defined as Offensive Efficiency minus Defensive Efficiency.

Offensive Efficiency is calculated as total points divided by Total Number of Possessions. Total Number of Possessions equals field goal attempts minus offensive rebounds plus turnovers plus .475 of free throw attempts. I’m not sure whether to agree or disagree on the number-of-possessions calculation, but I’ll defer to the nerds here.

Defensive Efficiency is a similar calculation: Opponent’s total points divided by Opponent’s Total Number of Possessions. Opponent’s Total Number of Possessions is opponent’s field goal attempts minus opponent’s offensive rebounds plus opponent’s turnovers plus .475 of opponent’s free throw attempts. Whew, that’s a lot of math with words.

Winning Percentage

Winning Percentage is a simple calculation of wins divided by total games played. Thank you.

Adjusted Win Percentage

Adjusted Win Percentage appears to juice the Winning Percentage based on where wins and losses occurred. Winning on the road is the most valuable (+1.4), while losing at home is the most costly (-1.4).  Home wins and road losses count as +.6 and -.6 respectively, presumably based on the notion that you don’t deserve a reward for doing what you’re expected to do. Neutral-site games are logged at face value. 

Scoring Margin

Scoring Margin is, as you’d expect, simply the difference between a team’s score and its opponent’s score. However, the point differential is capped at 10 points, and all overtime games are capped at 1 point.

I like that scoring margin is considered, and I like a cap, but I’d like to see some more data to determine whether 10 points is the best threshold for that to kick in. A one-point cap for overtime makes sense.

Here’s how all of that looks in infographic form:

https://twitter.com/marchmadness/status/1067063960753573889

The NET is a tool

Pardon the heading; I just wanted to make sure you were still reading. The NET isn’t actually a TOOL, but it is merely a tool, meaning it’s not the final word in NCAA Tournament teams or anything. It’s just one component of the selection process. The at-large teams will still be chosen by the selection committee, and the committee will still use a combination of analytics and human subjectivity to select and seed those teams. They’ll still use the team sheets, and the team sheets will still rely heavily on the quadrant system utilized for the first time last year. The primary difference is that the game results are now sorted into the quadrants based on NET ranking instead of RPI.

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Sam Hensley
Sam Hensley
2 years ago

Those numbers for home wins/losses vs. away wins/losses seem pretty out of whack to me. I can see a home win counting as 0.9 or maybe 0.8 wins, but 0.6 seems pretty bonkers to me. It should be interesting to see how the NET shakes out.

daetilus
daetilus
2 years ago
Reply to  Sam Hensley

Gotta agree with that. 0.6 seems a little harsh.

Not a math major anything, so I can’t tell exactly why those numbers were chosen. I think 0.8 (maybe even 0.75) seems a better choice. Which probably would mean the road portion would have to be adjusted down to 1.2 (or 1.25) to balance out

Gavin Driskill
Gavin Driskill
2 years ago

The primary issue is definitely the black boxiness of it.

Without any transparency, it will be accused of favoring mediocre Power Conference leagues at the expense of mid-majors, and probably rightfully so. The cynic in me thinks the NCAA isn’t going to let anything happen that impacts the bottom line of the tournament.

Gavin Driskill
Gavin Driskill
2 years ago
Reply to  Gavin Driskill

That said, as of this exact moment, here are the top 10s for NET vs. KenPom…

NET: UVA, Duke, Michigan, Texas Tech, UT, KU, Zags, Nevada, Sparty, Auburn
KP: Duke, KU, UVA, Michigan, Nevada, Zags, UNC, Sparty, Auburn, UT

On the one hand, perhaps it has decent calibration? On the other, if it largely copies other advanced rankings out there, what was the point?