Franalysis: What Are The Statistical Culprits For Iowa's Poor Defense During The McCaffery Era?

By houksyndrome on December 29, 2020 at 4:27 pm
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© Harrison Barden-USA TODAY Sports
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Fran McCaffery has been the head coach for the Iowa men’s basketball team for ten years, which is definitely long enough for interesting statistical trends to emerge.  I went looking on Ken Pomeroy’s website and compiled a variety of statistics in an effort to understand Fran McCaffery’s tenure at Iowa.  Fortunately, some interesting trends have emerged.  Today I'm going to discuss the defense and, in the coming days, I'm going to dig into some trends about Iowa's offense (which will be less depressing than this tome about our defensive issues).

Here is how Iowa has performed defensively, relative to its Big Ten peers, in a wide range of statistical categories.  The statistics are:

  • adjusted defensive efficiency (AdjD, points per possession adjusted by the quality of offenses that Iowa faces)
  • effective field goal percentage (eFG%, (2 pointers made + 1.5 * 3 pointers made)/field goal attempts)
  • opponent's turnover percentage (TO%, Turnovers/Possessions) 
  • opponent's offensive rebounding percentage (OR%, Offensive Rebounds/Missed Shots)
  • opponent's free throw rate (FTR, Free Throw Attempts/Field Goal Attempts)
  • opponent's shooting percentage on two pointers and three pointers (2P% and 3P%, respectively)
  • opponent's assist percentage (Assists/Made Field Goals)
  • blocked shot percentage (Blocks/Two Point Attempts)
  • percentage of opponents shots that are from three point range (three point attempts/field goal attempts)
Defensive Performance during the McCaffery Era
  2011 (11 teams) 2012 (12 teams) 2013 (12 teams) 2014 (12 teams) 2015 2016 2017 2018 2019 2020 Average Ranking Placement
AdjD 6 11 5 9 1 3 14 14 14 12 9.8 13th
eFG% 9 11 3 6 5 6 12 13 13 13 9.7 12th
TO% 3 9 5 3 6 4 5 13 5 7 6.4 4th
OR% 11 10 8 5 4 13 13 6 12 13 10 13th
FTR 2 5 5 5 5 1 3 5 6 6 4.6 3rd
2P% 10 12 5 10 3 9 12 13 13 13 11 14th
3P% 4 5 2 5 6 2 10 14 6 5 6.2 5th
Ast% 9 10 6 8 10 9 14 12 14 12 11 12th
Blk% 8 6 3 2 3 5 10 11 12 8 7.2 8th
3PA/FGA 8 8 6 12 9 13 12 10 13 11 10.9 14th

Shown are Iowa's rankings each season during the McCaffery Era, as well as their average ranking during the McCaffery Era and where that average ranking stacks up with the rest of the Big Ten ("Placement").  For example, Iowa's defenses have averaged 9.8th place in the Big Ten since Fran has been the coach, which is the second-worst average ranking of any team in the conference during that time frame (i.e. 13th in "Placement").  The fact that "Average Ranking" and "Placement" aren't identical might seem odd at first but it makes perfect sense.  Even the best program in the league, on average, isn't going to be #1 every single year so its average ranking will be worse than 1.  The same is true for the worst program in the league, which won't be 14th every single year and will thus have an average ranking better than 14th.  So, if you really want to see how well Iowa stacks up with its peers over time in a given category, "Placement" is the column to look at and not "Average Ranking."

As you can see, the defense has been, uh, not good.  Iowa's average defensive ranking of 9.8 narrowly beats out Nebraska to avoid being dead last in the conference (and Iowa beats them by a mere 0.02).  If you look at it year by year, Iowa was decent defensively in Fran’s first year, terrible the year after that, good when Gesell/Woodbury and Co. were around, and terrible ever since they left.  Sometimes perceptions and narratives are correct and, when it comes to Fran’s defenses at Iowa, well, they are correct.

By examining the component stats, it becomes easier to identify the culprits for Iowa’s poor defense.  Iowa actually does a pretty good job of forcing turnovers (4th best in the Big Ten) and keeping opponents off of the FT line (3rd best in the Big Ten).  Where they really struggle is keeping opponents off of the offensive glass and overall field goal defense (13th and 12th place, respectively).  The poor field goal defense is due entirely to poor defense against two point shots (14th place, i.e., dead last) and they are actually a respectable 5th place at defending three point shots (even if it doesn't feel that way when, say, Minnesota is draining 17 3s in a game).  Iowa's opponents attempt a larger percentage of shots from three point range against them than any other Big Ten team; however, they are slightly below average, accuracy-wise, on those attempts.

***The irony of me writing articles praising Iowa’s free throw shooting and three point defense a few days after that Minnesota game has not escaped my notice.***

In the past, I have noticed a weak inverse correlation between a team’s ability to keep its opponent off of the free throw line and its two point defense.  Intuitively, this makes a great deal of sense.  The more shots you contest, the worse your opponent is going to shoot but this will also lead to more fouls against you -- there seems to be something of a trade-off between these statistical categories and Iowa seems to be leaning too far in the direction of foul avoidance.

This lack of physicality may also contribute to Iowa's poor defensive rebounding (anecdotally, I often see Iowa fail to box out).  I have compiled detailed statistics, like the table above, for the offense as well and Iowa is actually the third-best offensive rebounding team in the league during Fran's tenure.  The fact that Iowa has been the third-best offensive rebounding team in the league and the second-worst defensive rebounding team in the league is striking.  Generally, the defensive player is the one boxing out so Fran’s failure to demand that in the players would be expected to manifest itself on the defensive end more than the offensive end.  However, I can’t conclude that this is the main culprit for our defensive rebounding struggles because I've found that there isn’t much correlation between a team’s defensive rebounding and its offensive rebounding, in general.  Here's a graph showing the national rankings for offensive (X axis) and defensive rebounding (Y axis) for each Big Ten team during the last twenty or so seasons (Fran’s Iowa teams are shown in orange).

Offensive and Defensive rebounding don't correlate for Big Ten teams

As you can see, there is essentially no correlation between offensive and defensive rebounding.  One simple reason for the lack of correlation is that different teams have different policies regarding how many players run back on defense versus crashing the offensive glass when a shot goes up.  From personal experience, I’ve played on teams that will send one player to the glass and I’ve played on teams that will send two or even three players to the offensive glass.  So, the disparity between the offensive and defensive rebounding performances could simply be Fran sending more guys to the offensive glass than other Big Ten teams rather than Iowa having players that are better at offensive rebounding than defensive rebounding and/or not blocking out, etc.  Or it could be a combination of both.  Iowa certainly isn't the only team whose defensive rebounding is a lot worse than its offensive rebounding (one year Minnesota was the best offensive rebounding team in the country and ranked 244th in defensive rebounding) but it sure would be nice if Iowa could fix that problem somehow.

The final statistic that I want to briefly discuss is defensive assist rate (the fraction of opponent’s made field goals that are assisted).  A large percentage of Iowa’s opponent baskets are assisted and this is a consistent trend year after year.  It’s not obvious what this statistic means:  it does not matter if a made basket is assisted.  However, I've found that defensive assist rate is consistent over time for a given team.  For example, Bo Ryan’s Wisconsin teams had the lowest defensive assist rate in the league every year from 2011-2015.  Ken Pomeroy has done some research ($$$) into this statistic and finds that lower defensive assist rates correlate with better overall defense and I have found the same to be true among Big Ten teams.  This makes intuitive sense in that assists are often symptomatic of a defensive breakdown of some kind:  fast break, dribble penetration followed by a dish for a dunk or catch and shoot three.  It's possible that Iowa’s high defensive assist rate is related to their overall poor defense due to these factors. 

However, Mr. Pomeroy has also found that zone defenses are often outliers in the relationship between assist rate and overall defense.  For example, in 2018, Syracuse had the 5th best defense in the country and were 351st in defensive assist rate (the highest in all of Division I).  Zone defenses also allow a large amount of three pointers.  2018 Syracuse was 338th in 3PA/FGA and they are like that year after year.  In John Chaney’s last season at Temple (his teams were famous for zone defense), their opponents actually attempted more 3s than 2s on the season, which may be the only time in D1 history that has ever happened.  The fact that Iowa has both a very high defensive assist rate and high 3PA/FGA rate makes me wonder if both stats may simply be due to Iowa playing more zone defense than the rest of the Big Ten.

Overall, it’s pretty clear that Iowa's defensive problems are due to allowing too many offensive rebounds and inadequate defense against two-point attempts.  I have found in the past that shot blocking correlates with two-point defense so improved shot blocking/rim protection might be a possible remedy; however, Iowa has been roughly league average at shot blocking under Fran, yet they're still the worst team in the league at defending two-pointers.  So it’s the two-pointers that Iowa doesn't block that have been nothing but trouble.  Personally, I think there are two likely culprits. One, Iowa has too many breakdowns leading to easy assisted baskets. Two, there's been an overall lack of physicality on the defensive end that manifests itself in the poor two-point defense, poor defensive rebounding and low fouling rates. Until Iowa begins to address those problems on the defensive end, the defense is going to struggle. 

Although Fran’s teams have generally been poor defensively, and this group of players has never posted a good defensive season, Fran has had very good defensive teams in the past so the situation is not completely hopeless.  With an offense like the one Iowa has this season, they don’t have to be great defensively, just respectable.  Is there a way to do that with the current roster?  I think so.  One obvious thing is to increase Joe Toussaint’s minutes.  My +/- data suggest that Iowa is dramatically better defensively when he is on the court.  Iowa can also play taller lineups.  The table below shows where Iowa has ranked among its Big Ten peers in height, both overall and at each position, for each season during the McCaffery Era.  I also included the average height ranking for the good defensive teams (2013-2016) versus all of the other years.

Iowa's Big Ten ranking in height
  2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2013-16 All other seasons
Total 4 3 1 1 2 3 5 1 4 6 10 1.75 4.71
C 7 12 6 2 3 2 12 4 6 4 4 3.25 7
PF 6 9 3 1 3* 2 9 1 3 6 4 2.25 5.43
SF 5 4 1 2 1 5 2 1 3 7 9 2.25 4.43
SG 2 1 1 1 2 8 1 1 2 10 11 3 4
PG 5 2 6 3 4 4 9 9 4 10 12 4.25 7.29

As you can see, Fran’s teams have tended to be among the league’s tallest, especially those 2013-2016 teams which were generally pretty tough on defense.  In particular, check out the 2015 team which had the best defense in the Big Ten according to Ken Pomeroy’s algorithm.  That team’s starting five was generally Mike Gesell, Peter Jok, Jarrod Uthoff, Aaron White and Adam Woodbury, with Anthony Clemmons, Josh Oglesby, Gabe Olaseni and Dom Uhl coming off the bench.  That is a LOT of height, particularly in the front court. Iowa was the tallest team in the Big Ten (and the nation) at the SF position and, at PF, they were the 5th tallest team in the country that year (despite being only the 3rd tallest in the Big Ten).  Iowa was also very tall at SG that year too, with Jok and Oglesby logging major minutes.  Iowa could try and mimic that team with the current roster.  That might mean no longer trying to use Connor and Wieskamp at PF and using Keegan Murray and Pat McCaffery at that spot instead.  Preliminary +/- data suggest that Pat and, especially, Keegan improve Iowa defensively.  I would not move Fredrick or Wieskamp out of the starting lineup, but Fran could slide Wieskamp over to SG when Fredrick sits, which he already does to some extent.  Iowa could also experiment with a Toussaint / Connor McCaffery rotation at PG, which would be a defensive improvement over the current Bohannon / Toussaint rotation at that spot.

This is not without risks. While in a slump, Bohannon has been an offensive flamethrower in the past so it’s tough to stomach the idea of benching him, especially given all of the injuries that he’s battled through to play this season.  It’s also worth noting that the 2018 team was extremely tall and extremely horrible defensively.  I think that team is an outlier, though.  Bohannon was the only PG on that roster (due to Connor’s illness and injury-related absence).  That team had Nunge and a wounded Baer trying to play SF.  Cook was a non-factor as a shot blocker at PF despite his size/athleticism combo.  Garza’s defense has improved by leaps and bounds since then.  The bottom line is that I think this roster has tall players who are much better defensive forwards than that 2018 team, to say nothing of the fact that it also has Toussaint as an option at point guard.  I think this team has some of the same roster pieces that Fran’s good defensive teams have had in the past, so there is hope. We'll see what the defense is able to do over the next few weeks. 

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