The Championship Arc makes its 2021 debut

If you want to know which men's basketball team is going to win the 2021 NCAA Tournament, here's a good place to start

Two years ago this month, while researching decade-old college basketball efficiency ratings in the backyard of Chicago’s Big Ten Team, I stumbled into a concept that can help predict who will cut down the nets at the end of the NCAA tournament. As I clicked through every year of’s database, I plotted the pre-NCAA tournament adjusted offensive and defensive efficiency ratings for every Final Four team from 2002 through 2018 on a scatter plot.

For the uninitiated, – or just “KenPom” – is every men’s college basketball writer’s guilty pleasure. The site provides tempo-free, efficiency-based statistics because society has progressed past the point where someone could look at Virginia’s offense in 2019 – when the Cavaliers scored only 71.4 points per game (210th nationally) – and then try to downplay their ability to score, simply based on their per-game scoring average. When adjusted for how fast or slow every team in the country played that season (Virginia played at the slowest tempo nationally), as well as the quality of each team’s opponents, the Cavaliers’s offense was the second-most efficient nationally that season – far better than 210th. The “adjusted” part of “adjusted efficiency” accounts for tempo, quality of opponents and when games were played.

At the time of my research, my goal was to find historical comparisons for some of the best teams in the country during the 2018-19 season so that I could draw parallels, like “Michigan State’s adjusted efficiency margin this season is similar to that of North Carolina in 2005,” and I would have the data to back it up. That might’ve made for a decent college basketball story on a sleepy Tuesday afternoon in January.

But I quickly realized that when you plot the offensive and defensive efficiency ratings for past national champions during the KenPom era, most of them quite literally fall under the same category. Using 2018 Villanova (elite offensively) and 2013 Louisville* (elite defensively) as the two end points, you can draw an arc under which 13 of the last 18 national champions fall, based on their efficiency ratings.

It might even be 14 of the last 18 champs if you’re generous in how you draw the arc.

I called it the Championship Arc.

The Championship Arc measures efficiency margin

What the Championship Arc contextualizes is adjusted efficiency margin, or in other words, how much greater a team’s offensive efficiency rating is compared to its defensive efficiency rating. Efficiency margin measures by how many points a team outscores its opponents, on average.

Fourteen of the last 18 national champions have had a pre-NCAA tournament adjusted efficiency margin of at least +25.00 points per 100 possessions. The four champions that didn’t were UConn in 2011 and 2014 (pre-tournament adjust efficiency margins of +21.7 and +19.1, respectively), 2003 Syracuse (+19.9) and 2006 Florida (+23.9). For context, if a team with an adjusted efficiency margin of +25.00 plays a 69-possession game, which is roughly the national average for possessions per game this season, then that team would be expected to outscore an average opponent by roughly 17.3 points on a neutral court.

It’s important to evaluate past national champions based upon their pre-NCAA tournament efficiency ratings because, obviously, a team that makes the Final Four will be required to both (a) play good basketball and (b) beat good teams, so even though KenPom provides predictive metrics that analyze how teams are expected to play in the future based on their past results, evaluating past national champions and other Final Four teams based upon their end-of-season numbers would actually be skewed by hindsight.

It’s not a perfect comparison, but it would almost be like examining lottery winners’ bank accounts after they had won the lottery. If you wanted to know what tax bracket the next lottery winner might come from, you wouldn’t want those eight or nine-figure payouts to affect your analysis. We want to know who a team was on Selection Sunday, not who it was when “One Shining Moment” was playing and when confetti was falling.

Of course, the Championship Arc is not a hard-and-fast rule – it’s more of a strong suggestion. The lowest pre-NCAA tournament adjusted efficiency margin of a Final Four team during the KenPom era was 2011 VCU at just +8.75 points per 100 possessions, when VCU started the NCAA tournament by playing in the First Four and it advanced all the way to the Final Four. The Rams finished the season with an adjusted efficiency margin of +13.49, so their six NCAA tournament games increased their season-long efficiency margin by nearly five points (once again showing why we need to evaluate teams on their pre-tournament, not post-tournament, ratings.)

For perspective, a team with an adjusted efficiency margin of +8.75 this season would rank No. 89 nationally on, through Jan. 21, so almost any team in the top 100 this season could point to a Final Four team from last decade as proof that it, too, can make a Final Four run, but VCU is the exception, not the rule.

Let’s see some receipts for this concept

The Championship Arc made its debut in a story I wrote for Stadium two years ago, and I wrote a follow-up story before the 2019 NCAA Tournament that identified a group of nine teams that I said would include the eventual national champion. Six of those nine schools made the Elite Eight and one of them, Virginia, won the 2019 national title, holding up the fortune-telling ability of the Championship Arc in its inaugural season.

The 2019 national championship game between Virginia and Texas Tech went to overtime, which nearly sent a men’s basketball national championship trophy to Lubbock, Texas, and it almost led to me taking a self-imposed ban from Excel if the Championship Arc started 0-for-1, but the arc had also allowed me to identify the Red Raiders before the start of the NCAA tournament as a potential exception to the rule:

A few teams, like Texas Tech and Virginia Tech are just outside of the arc. The Red Raiders have the No. 1 defense in the country and the Hokies have the No. 8 offense but it’s each team’s play on the other end of the floor that leaves them just outside the arc.

Texas Tech’s offense is much-improved in the last month and it’s ranked No. 34 in terms of efficiency. Virginia Tech’s defense is ranked No. 32 nationally, so the Red Raiders and Hokies are two prime candidates of teams outside of the Championship Arc that could theoretically win the national championship.

Virginia Tech, the other team identified as a potential exception to the rule in 2019, nearly beat No. 1 overall seed Duke in the Sweet 16.

While there obviously wasn’t an NCAA tournament last season, the Championship Arc identified Kansas and Gonzaga as the favorites, with Dayton, Duke, San Diego State, Michigan State and Baylor making up the second tier of contenders that fell just outside the arc. After the men’s college basketball 3-point line was extended prior to last season, the national average for 3-point percentage dropped from 34.4 percent in 2019 to 33.3 percent last season, so you can probably chalk up the limited number of teams inside the arc to the slight drop in outside shooting.

That brings us to this season.

Ken Pomeroy has explained that the influence of his preseason ratings will no longer affect his site’s current ratings starting on Jan. 23, which is tomorrow:

And it’s not like the ratings will be any different on January 22 than January 23. By the time mid-January arrives, the influence of the pre-season ratings will be tiny compared to 15-20 actual games that will have been played by each team.

While acknowledging that the number of games played this season can vary significantly from team to team, and that even a 10,000-foot analysis of this season might be imperfect due to the pandemic, here’s how the top 15 teams on KenPom stand in relation to the Championship Arc through Jan. 21.

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In relation to the Championship Arc, Gonzaga and Baylor both currently stack up as favorably as almost any Final Four team since 2002, while the next-best teams – Villanova, Michigan and Iowa – are on the edge, or just outside, of the arc.

The collective status of the Bulldogs and the Bears in relation to the rest of the sport raises a potential “Would you take Gonzaga and Baylor versus the field?” debate. Through Jan. 21, Gonzaga’s adjust efficiency margin is +32.94, just ahead of Baylor at +32.79, while Baylor’s margin is more that 5.5 points per 100 possessions better than Iowa (+27.08).

For what it’s worth, here are the two most recent seasons in which the final, pre-NCAA tournament efficiency margins of two best teams in the country were both a) separated by roughly one point per 100 possessions, or less, and b) the second-best team’s efficiency margin was more than three points per 100 possessions better than the third-best team in the country:

  • 2010: Kansas (+32.5), Duke (+31.5), Syracuse (+27.6)

  • 2005: Illinois (+33.3), North Carolina (+32.0), Duke (+28.7)

In 2010, while No. 1 seed Kansas was upset by Northern Iowa in the second round in part because of one of the most iconic shots in recent NCAA tournament history, Duke won the national championship.

In 2005, North Carolina and Illinois met in the national championship game as No. 1 seeds and the Tar Heels won a five-point game. So, in the admittedly small sample size above, three of the last four teams that have been part of a clear, two-team upper echelon in a season have advanced to the national championship game.

Maybe the Gonzaga and Baylor vs. the field debate isn’t as hot take-y as it may have sounded at first.

Gonzaga and Baylor were supposed to play in Indianapolis in early December but the game was canceled due to positive COVID-19 tests and it would be fitting if the top two teams in virtually every rankings system wind up meeting in Indianapolis in the NCAA tournament.

What can change between now and Selection Sunday?

The aforementioned Texas Tech squad from 2019 is a prime example of why a midseason Championship Arc update is both instructive and also not definitive. The Red Raiders’s adjusted offensive efficiency ranked No. 140 nationally on Jan. 28, 2019, so despite them having the No. 1 defense in the country at the time, they were incredibly far off the radar, in relation to the Championship Arc (see below).

But by the time Selection Sunday rolled around, Texas Tech’s offense had climbed to No. 34 nationally, which put the Red Raiders just a hop, skip and a jump from the Championship Arc, as they cemented their status as a dark-horse national championship contender and they were ultimately only a shot or two from winning the championship.

So, the efficiency ratings of college basketball teams through late January are certainly not final, especially this season, when some teams didn’t play their first game until January. Texas Tech, ironically, or perhaps predictably, is in somewhat of a similar position to where it stood on Selection Sunday in 2019, as it currently has the No. 4 defense but No. 34 offense.

Every March, you’ll hear analysts describe how a team needs to have a strong balance between offense and defense. A team probably needs to be ranked in the top 20, 25 or 30 nationally in both offense and defense in order to win a national championship, some prognosticators will say. While that’s not a bad rule of thumb, it’s also not as specific as it could be. From one season to the next, having the No. 30 offense might not mean the same thing and the Championship Arc can help pinpoint just how realistic are a team’s national championship hopes, especially when there’s a massive imbalance between its offensive and defensive performance.

After Indiana upset No. 4 Iowa in Iowa City on Thursday night, while scoring 81 points and holding the Hawkeyes to a season-low 69 points in 68 possessions, Iowa’s adjusted defensive efficiency rating climbed to 97.3 points per 100 possessions, which ranks 90th nationally. Its defensive ranking fell 17 spots on Thursday, and despite having the No. 1 offense in the country, the Hawkeyes fell outside of the Championship Arc after the loss.

But they’re certainly not alone as a team that is really good, if not elite, on one end of the floor, while its play on the other end lags behind.

Tennessee’s defensive efficiency ranks second nationally, but its offensive efficiency is No. 54, and Clemson’s defense sits at No. 19 compared to an offense that ranks No. 76. VCU’s defense (No. 26) is ranked nearly 100 spots higher than its offense (No. 125).

Ohio State’s offense/defense splits are No. 5/No. 72 and LSU’s are even more dramatic – No. 6/No. 127.

All of those teams have a little less than two months to increase their efficiency margin and in the process, decrease the gap between where their offensive and defensive efficiency ratings are ranked.

Because history says the Championship Arc is a pretty strong indicator of which teams belong in the elite group that can truly expect to contend for the national championship, and which teams that fall outside of the arc will likely see their national title aspirations get left out in the cold.


Recap of the last newsletter

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“Why has the college basketball community seemingly moved on from asking questions about Keyontae Johnson’s health status, what caused it and what it might mean for college sports?

“Like the question itself about what led to Johnson currently being a coach on Florida’s bench rather than one of its players on the court, that’s a question that’s worth asking more often.”

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