The most important statistic in basketball (and how it's killing us)

One of the great strengths of four-factors analysis is that it illustrates how important basketball skills other than shooting the ball are to playing successful basketball.  Taken together, limiting turnovers, crashing the offensive glass, and getting to the free throw line can more than offset a bad shooting night (with the converse being true on defense).

At the end of the day, though, shooting the ball is still the single most important component of statistical basketball performance.  In the words of Dean Oliver:

The game of basketball was set up that way more than one hundred years ago, where the objective of that first game in Massachusetts with two peach baskets was nothing more than getting the ball into those baskets. In that essence, the game hasn't changed. Whether it's 3-foot shots or 3-point shots, shooting the ball from the field remains the dominant means of scoring points before giving it back to opponents.

Of course, the term "shooting the ball," as applied to offensive performance, is something of an oversimplification.  Not all shots are created equally.  The greatest pure shooter in the world won't have much success if he's consistently being forced to take fade-away 18-footers from the corner.  The effective field goal percentage an offense posts is, therefore, reflective of both the kinds of shots a team takes and how proficient it is at sinking those shots.

A couple years ago, I had a minor eureka moment in thinking about this topic:

Offensive effective field goal % is subject to the problem Pomeroy notes above: It tells you how good a team is at scoring the basketball (when it doesn’t turn the ball over), but it doesn’t tell you whether the ability to score is the result of (1) creating and taking good shots or (2) simply being a good shooter.

With defensive effective field goal %, on the other hand, it’s a good bet that pure shooting ability is pretty randomly distributed across a team’s opponents. So a low defensive effective field goal % indicates a team excels at forcing its opponents to take difficult shots.

My assertion, then, is that defensive effective field goal percentage is the most important basketball statistic in determining team-level success.  It has the greatest statistical weighting relative to overall defensive efficiency, and it's more easily interpretable than offensive effective field goal percentage.  Simply put, it tells you, "Does this team consistently force it's opponents to take difficult shots?"  Teams for which the answer to that question is "Yes" are going to have a pretty decided advantage whenever they take the court.

Unfortunately, this conclusion makes the graph below particularly unpleasant for MSU fans:

After holding all of their first six conference foes to an eFG% below 50%, the Spartans have now allowed 5 of their last 6 opponents (including the last 4 opponents consecutively) to top that threshold.  The result, of course, has been a quick return to the Big Ten pack after building a 3-game lead halfway through league play.

It's hard to point to any single factor driving this defensive turn for the worse.  The schedule has played a partial factor; 4 of the last 6 games have been on the road, and 4 have been against teams with top-50 offenses (per KenPom).  But the dramatic shift upward in the data plot above is bigger than can be explained by just the quality of the opposition.

For whatever reason, MSU's defense just hasn't been as stingy in forcing tough shots in recent games.  Opponents have certainly come out blazing hot from beyond the 3-point arc in the last several games.  The last 4 opponents (Northwestern, Wisconsin, Illinois, Purude) have combined to shoot .400 from 3-point range.  But MSU has also struggled to stop opponents from getting easy looks around the basket.  Those same 4 opponents have combined to shoot .575 on 2-point attempts. 

A pretty diverse set of scorers has lit the Spartans up of late.  All of the players below have taken at least 8 shots from the field and posted an eFG% of at least 50% against MSU in the last 4 games:

  • John Shurna
  • Jason Bohannon
  • Keaton Nankivil
  • Demetri McCamey
  • D.J. Richardson
  • E'Twaun Moore
  • JaJuan Johnson
  • Robbie Hummel

That's 4 guards, 2 big men, and 2 floaters (Shurna/Hummel).  So you can't pin the defensive struggles on any particular defender--or even group of defenders.  It's been a team-level failure.

We can hope that some of it's been a little flukey.  McCamey and Moore just seemed like they couldn't miss, no matter how good the defense was.

And maybe some of it's stemmed from strategic problems.  Joe Rexrode reported the following today:

Based on some of the comments from MSU's players last night, Matt Painter tweaked some things with his offense, turning screeners into backdoor cutters at times, and that caught the Spartans off guard. That doesn't excuse all the slow reaction, bad communication and Purdue layups, but it sounds like the Boilermakers hit the outside corner with some curveballs.

Still, 4 consecutive conference games--and 5 of 6 games--is a decent-sized sample by college basketball standards.  I don't have any great working theory as to exactly what needs to be corrected on defense to reverse the recent trend--except to say, "everything."  There have been too many open 3-point looks, easy baskets off the pick and roll, breakaways conceded off turnovers, and mid-range floaters allowed in open space.

We talked (briefly) yesterday about how Tom Izzo's defensive scheme is designed to utilize help defense to prevent easy looks at the basket.  As important as defensive eFG% is for any basketball team, it may be even more important for Tom Izzo teams.  Creating turnovers will never be a big strength for MSU, and you can't rebound the ball if the other team doesn't miss.  (One defensive positive: up until last night, the Spartans have continued to avoid sending their opponents to the free throw line and now rank 14th in the country in opponents' free throw rate.)

There's no bigger sports "cliché" then "defense wins championships," but it sure seems like it will be the case this time around.  As disjointed as the offense has looked of late, the team has scraped together enough points to stay in games, and scoring efficiency should improve as Kalin Lucas gets healthier.  The question is whether Izzo can get the MSU defenders working together again to keep opponents from scoring so many points that what the team does on offense becomes fairly irrelevant.

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