Is Fouling Correlated with Good or Bad Defense
There has been a long-held belief in basketball that great defensive teams don’t commit many fouls.
In fact, many sages of the game have endorsed this approached adamantly: Gregg Popovich, Bo Ryan, Tony Bennett, Mark Few, Brad Stevens, etc. And of course this philosophy makes sense; fouling puts opposing teams at the foul line, gets our team into foul trouble and can put us in the bonus for long durations of time. This was a belief I held tightly as well, that was until one day I was reading “Swing Your Sword” by Mike Leach and uncovered a study in football that caused me to question the entire thing. Is fouling really correlated with poor defensive teams?
*This article was written in Dec 2020 - all stats and rankings referenced are from that year.
The Correlation between Fouling and Team Defense
First, if you don’t know who Mike Leach is, he’s the head coach for Mississippi State football and known as beginning one of the games most out-of-the-box thinkers. His book “Swing Your Sword” is great. In one section Leach talks about his believes towards penalties and defense. He argues that the teams that commit the fewest penalties in football are often the worst teams in their leagues. He relates a lack of penalties to a lack of aggression and toughness, not the use of great technique and execution. He would never make it a point to eliminate all penalties.
Of course, these are comments taken from a coach best known for his offenses. But then I found a study by Jim Reese titled, “Inside the Hash Marks,” that compiled data from over 400 NFL, college and high school football games to discern the effect penalties had on winning games. “The results were both enlightening and conclusive.”
“The results showed that high school teams having more penalty yards in a game won two-thirds of those games (67%), while college teams with more penalties won approximately half the time (52%). But NFL teams won only 45% of the games in which they were assessed more penalty yards than their opponents.”
The study even showed a positive correlation to winning margin and penalty yards. Meaning that the team that committed more penalties actually showed an increase in their margin of victory as compared to a team who won and did so with a close penalty margin.
The study made me think that Leach could be on to something here. So I began to look for a similar study for basketball. As you may expect, I couldn’t find any. So, I ran the data myself.
A quick look at this year’s NBA Defensive Efficiency rankings and Team Fouls began to look suspicious. 4 of the top 5 defensive teams ranked in the top half in fouls per game.
Team Def Rank Foul Rank Bucks 1 8 Raptors 2 21 Celtics 3 20 Lakers 4 16 Clippers 5 28
You can see that it is even more extreme; the Celtics, Raptors and Clippers were top 5 in Def Eff and yet bottom 10 in fouls per game. In fact, the Clippers fouled the 3rd most times in the NBA and still ranked 5th in Def Eff.
But what about the worst defensive teams, surely they fouled a lot too:
Team Def Rank Foul Rank Spurs 26 5 Hawks 27 30 Trailblazers 28 24 Wizards 29 29 Cavaliers 30 1
Well, this makes a little more sense, the two most foul happy teams in the league were bottom 5 in defense. But, there are still two teams in the bottom 5 that committed league highs in not fouling. So what about college?
NCAA Def Rank Foul Rank (353 Schools) Virginia 1 2 Memphis 2 299 Kansas 3 11 Wichita St 4 251 Baylor 5 138 … Holy Cross 349 186 W Illinois 350 219 Houston Bap 351 318 TN Martin 352 93 Chicago St 353 339
Again, there is some that makes sense; UVA and Kansas had great defenses and almost never fouled. But there are also outliers: Memphis and Wichita also had great defenses but fouled at extremely high rates. So what’s the correlation getting at?
Well, to truly understand that we must get rid of the rankings and look at the raw numbers. Below are the graphs of the NBA and the NCAA over the last 5 seasons. Realize that the lower your Def Eff number, the better the team’s defense. So the data points to the left of the graphs reflect the best defensive teams.
As the dominating dogma would suggest, the trend line does slope up, meaning that the more fouls a team committed the worst their team defense was. However it is interesting to note the correlation coefficient (this one for the math nerds) for these data sets. The correlation in the NBA was 0.194 and the correlation in the NCAA was 0.177. Just for reference the correlation coefficient is a range between -1 and +1, and unfortunately such a low correlation can’t be deemed significant.
So although there is a slight trend towards the preexisting belief that eliminating fouling will lead to better defense, we cannot conclude that this is at all definitive. We have already seen many outliers in just the past year.
Unlike in football, these findings were not conclusive. Perhaps enlightening, but definitely not conclusive. If anything, we have confirmed that there are many paths to great defense.
Personally, I tend to side with Leach. I rather pull back the rains of physicality and aggression than try to will and push a team to those points. Of course we always will want to get rid of silly fouls, not all fouls are created equal, but we also must be careful about muting the contact that great defense requires.
There is no conclusion here, just a better understanding that fouling should not be viewed through a black or white lens. It is definitively a gray area. Whether you choose to live with the fouls of a physical defense or pursue the precise execution of eliminating the officials from your defense, it is possible to reach greatness.