Measuring Defense

As DBSF has exhausted much of his take on the peculiarities of the NBA and the styles and idiosyncrasies of certain players and their subcultures, it's time the blog goes in a different direction. Absent an Adam Morrison return to the NBA or JR Smith and Andray Blatche teaming up to lead a team to a first round, four loss, zero win playoff series in which each is suspended at least once for conduct detrimental to the team, this move will have been long over due.

The new focus will rely more on analytics, and for the foreseeable future the focus will be to identify the best defensive player in the NBA. This approach will demand more original analysis, which will also be more time consuming and result in less frequent posting. Finding the appropriate measure(s) of defense won't be accomplished in a single analysis and likely demands re-configuring and fine-tuning previous models. But--and depending upon the available data (this is key)--the goal is to establish some measure that in addition to a range of conventional defensive statistics as well as the other existing 'advanced' defensive statistics grants greater insight on a player's value. (Admittedly, this is no way a novel endeavor.)

But why defense? And, don't we already know who are the best defenders? To answer the first question, it's 50% of the game and gets maybe 5% of the attention on a good day. To answer the second, the NBA All-Defensive team is certainly a start. However we cannot be confident that All-Defensive nominees don't benefit from having superior defensive teammates and, thus, help defenders. Consider Dwight Howard at his prime. He was such a defensive presence in the paint that guards on the Magic could assume far greater risk on the perimeter and attempt to challenge more threes and perimeter shots because even if their man gets by them he still had to convert in the lane with Howard, arguably the best shot blocker in the last decade, contesting. In other words, Dwight Howard's aptitude as an interior, help defender might have made all of his teammates appear as better defenders.

Then what about conventional measures of defensive achievement, like steals or blocks? Both are undeniably important as one ends the opponent's offensive possession (steals) and the other potentially ends the possession or at least negates a potentially made field goal (blocks). But both demand the defender to assume risk, where undesirable outcomes include fouling or missing the steal and granting the opponent more direct access to the basket or missing the block and being out of position for a defensive rebound, which is a critical conventional measure of defensive aptitude because the defensive rebound absolutely ends the opponent's possession.

Take Allen Iverson, a three-time NBA steals leader, who was All-NBA first team 3 times, second team 3 times, and third team once but was never voted to an All-Defensive first or second team. There are likely many factors that explain this but consider Iverson's success in steals. While his great quickness would be an asset on perimeter defense, his 6'0" 165 pound frame becomes a liability the closer the offensive opponent draws him to the basket. As a result, it would be in Iverson's best interest to assume risk and attempt more perimeter steals (and, thus, increase his steal average) at the cost of sacrificing  interior defense where his physical size would prove ineffective.

So was Iverson a good defender or not? That's what the following posts will hopefully uncover. It may be that he was an excellent perimeter defender but a mediocre to poor defender inside the three point line--so we need to know where Iverson was on the court to answer if he was a good defender or not. Unfortunately, although NBA teams are collecting the spatial data necessary to conduct such analysis, they are not sharing it.

As a result, most "advanced" measures of defense reflect formulas that attempts to standardize one or more conventional defensive statistics, or they look at things, like the points allowed while the player was on the court. The latter is certainly an important indicator of all around defense however it is necessary that the measure accounts for the defensive aptitude of a player's teammates and the offensive ability of his opponents. (In other words, if a defensive player is stuck with four JR Smiths for teammates and is playing against the Heat and Thunder every night, then it's not fair to say he's a bad defender because his team gives up a lot of points.)

So what categories should define a defensive player? One was mentioned--defensive rebounds because it effectively ends a possession. Second, opponents' turnovers while the player was on the court. Many steals or poor offensive decisions (resulting in TOs) occur because of otherwise non-quantifiable defensive plays, like hustle, active hands, and quick help defense. Third--and this is likely the most difficult data to access--time left on the opponent's shot clock per their possession. This would have to be standardized by opposing team because some teams aim to shoot earlier in the shot clock than others. This measure would show which players (or teams) cause opponents to take more time to shoot than they do on average, which likely captures successful on-ball and help defense. All of this has to be standardized by minutes and position (and maybe size) as we wouldn't expect similar defensive rebounds from a center and a PG.

One limitation that's worth recognizing is that even if some useful measure of defense is determined it will only allow comparisons within cohorts of players. So, you could compare LeBron with Ibaka but you couldn't compare LeBron with Jordan. Besides the fact that rule changes over the years can affect a player's output (there is no better example of this than in the NFL where the restrictions on defensive backs have enabled QBs to shatter records in recent years), it would require comparing a line of cohorts to establish some inter-generational standard.

In other words, you'd have to do something, like compare a cohort of young players that played with Jordan (say Rasheed Wallace and Kevin Garnett) to a next level cohort (say Kenyon Martin and Tyson Chandler) and then compare how LeBron played against them while controlling for age and other factors. So you could say based on how LeBron plays against Tyson Chandler and based on how Chandler played against Rasheed Wallace and based on how Wallace played against Chris Webber and based on how Webber played against Dan Majerle and based on how Majerle played against Jordan we could expect LeBron and Jordan to match/ not match defensively? Obviously too much uncertainty (or, "noise") arises across generations so any attempts to standardize defensive performance will be relative to probably a 3-5 NBA season period.