HAALAND: Defensive decline

As Iowa State has struggled over the past few weeks, it has been apparent if you’ve been following the progression of the season’s numbers that the defensive end has been the root of the struggle far more than the offensive end. The offense has clearly not been perfect, has its issues, and can get stuck in ruts if shots aren’t falling, but the KenPom offensive efficiency has been climbing for weeks. That climb has not just been by rank with other teams falling but the value has steadily improved.

But the defensive end has been a different story. It was just a few weeks ago that the defense was still in the KenPom top 25, but now it has slipped all the way to No. 49. So what gives?

I looked into it and found the key culprits but also a few cumulative issues that are compounding into regressing defensive numbers.

To dig into this I broke out Iowa State’s first eight Big 12 games plus Mississippi and compared them to the last eight games. For the most part, right after the home thumping of West Virginia was the start of the steady decline.

First things first, I used to look at the AdjO and AdjD by game to confirm my initial thinking that this has indeed been a defensive issue. I averaged the game AdjO on his site for the first nine and last eight as well as the AdjD. In the first nine games, ISU’s AdjO averaged to 1.172 ppp and in the last nine it jumped to 1.212. But, the defense slipped from 0.914 in those first nine games all the way to 1.034 in the last eight. Theory confirmed, but why?

Again, I broke out the first nine games versus the last eight to try and figure things out. I have Iowa State’s offensive numbers there just for reference, basically, but I’ll primarily focus on the defense.

The first thing I noticed was the opponent 3-point percentage which goes back to this Twitter conversation I had with the incomparable Travis Hines on January 3rd where we discussed opponent’s 3-point percentage and the rate at which the Cyclone defense allowed them to be shot:

Better shooting

If you don’t know, the basic theory by some basketball-math nerds is that opponent 3-point percentage is more random than not, and the defense does not have a ton of control over opponent jump shooting accuracy. The best 3-point defense is achieved by limiting the attempts and for the most part, a team’s success defending the collective opponent’s accuracy from the 3-point line is, random. Agree or not, the point of the conversation that I had with Travis was pointing out that the Cyclone defense tended to allow opponents to shoot 3-pointers at will and up to that point had been on the good side of the random stick.

That’s a really long-winded way to say that opponents in the first nine games hit on almost 33 percent of 3-pointers and in the last eight that has jumped to 38.5 percent. The opponent 3-point attempt rate has been steady at 36 percent and the Cyclones are currently allowing the 221st most attempts in the country.

From the chart above, you’ll notice the spike in effective field goal percentage largely due to the 3-point percentage already discussed but opponents are also shooting better inside the arc, even if not drastically so.

Opponents are also making more shots near the rim by making 56.5 percent of dunks and layups when they were making just 51.4 percent in the first nine games. But one interesting note is the percentage of 2-point attempts that have been dunks or layups has dropped from 39.8 percent to 33.8 percent. More on that later.

But improved shooting isn’t the only story.

Opponents have improved their turnover rate, offensive rebounding rate, they’re getting to the free throw line more often, and they’re shooting a higher percentage when they do get to the free throw line. There is kind of a lot going on here, but hang in there…

More scoring chances

One stat I like to follow tracks net scoring chances for teams to account for the differences in offensive rebounding and turnovers and how teams rely on each both offensively and defensively. In the first nine games based on how Iowa State limited offensive rebounds and forced turnovers, opponents had scoring chances (field goal attempts or trips to the free throw line) on 96 percent of possessions. That number probably lacks relative context for most people but in the last nine games teams have had netted more scoring chances the possessions at just over 100 percent, all because the turnovers have slowed and the defensive rebounding has gotten worse.

Free throws

From the chart above, the opponent free throw rate (FTA/FGA) has jumped almost four percent but aside from getting there more often, opponent’s also made three percent more of their attempts in the last eight games versus the first nine (another less controversial opponent shooting stat that is random).

So what do all of these numbers mean, practically? See below (note that “CL2” = close 2-pointers and “Oth-2” = non-layups and non-dunk 2-point attempts):

The makes and attempts per game is in each row along with the average points per game from each shooting stat and then summed at the bottom.

Keep in mind that this doesn’t account for tempo and possessions have dipped a bit in the last eight games. In the first nine games, the average pace was 69.2 possessions while the last eight games have dropped to 67.2 possessions. On average, Cyclone opponents have scored 6.5 more points per game on two fewer possessions.

The final word

The defense was probably never as good as it appeared earlier in the year when it was KenPom top 25; with the allowed attempt rate from the 3-point line and the percentage that opponents made early on. The improved opponent free throw percentage also balances out the first nine games to essentially land near the national average. A regression appeared unavoidable and we’re living through it right now.

Aside from the shooting, the turnovers have dropped and the rebounding has to get better to eliminate the extra scoring chances.

The Cyclones are committing fewer fouls per game on average but remember that decreased rate of shot attempts at the rim? You have to wonder if that decline is very directly related to the increase in trips to the free throw line by being called for more shooting fouls than in the first nine games. This could very well also be tied to the amount of dribble penetration that has been allowed.

In my opinion, this is largely a problem of dribble penetration being allowed that has caused the defense to rotate out of position, help too slowly, over help when it shouldn’t and all of this leads to worse defensive rebounding, more fouls at the rim, and the opponents continuing to get whatever 3-point attempt they’d like while making a whole lot of them of late.

All of this evidence doesn’t unequivocally prove that conclusion but it’s hard to argue against those numbers and what our eyes have seen.