NBA HD: Dismantling the Assist

Sometimes we need to take a step back from it all and ask ourselves fundamental questions to find truth in our lives.

Today, we will have one of those moments.  Ask yourself this question:

Why do we care about assists?

I’m not saying we shouldn’t care about assists.  We should.  They tell us something, which is valuable.  But what exactly do they tell us?

An assist tells us when a player passed to someone and that pass lead directly to a made basket, but only it should only be recorded if the basket is made.  It is recorded in attempt to reward good passing.  Say Steve Nash passes to Jason Richardson who immediately nails an 18-footer from the wing.  Nash receives a token for his efforts in the form of a recorded assist.  The thought process being that we should award Nash some credit for Richardson’s made basket because he had something to do with that ball going in.

The assist represents an example of post hoc reasoning, or post ergo propter hoc. Translated into English, it means “after this, therefore because (on account) for this.”  When this reasoning is incorrectly applied, it is referred to as the post hoc fallacy, which you’ve probably heard before.  The post hoc reasoning (or fallacy) states that if one event followed another, then it must have been caused by the original event.  A pass led to a bucket and therefore, it was a good pass.

Here’s where that reasoning becomes problematic.  How many times have you seen a player make a magnificent pass to a teammate, only for the teammate to subsequently blow it on the shot?  Countless times, I bet.  And how many times have you seen a great pass on a highlight reel where the player misses the shot? Almost never, right? We allow the shot result to influence our perception of the quality of the pass.  An outstanding pass transforms into highlight reel material or an assist only after the ball goes through the net.

Consider the following clip of Pau Gasol and Kobe Bryant:

Pau Gasol gets credit for only one assist because Kobe Bryant blew the dunk in the first play.  In reality, both passes were equally worthy of record.  When we speak of good passes or passes worthy of record, we’re subconsciously referring to passes that increase the chances of scoring from Moment A to Moment B.  In the first play of the clip, the chances of scoring when Pau Gasol has the ball 25 feet away from the rim (Moment A) pales in comparison to the chances of scoring after he rifles the pass to Kobe (Moment B).  Rather than changing it’s mind ex post facto, the ideal assist should try to capture that expected difference regardless whether Kobe Sprites it or not.

What we’re really after is the potential assist; a pass that directly leads to, not a made shot, but an attempted shot.  For some shots, a good pass is vital.  For others, the effect of a pass is negligible; the shooter would have made it anyway.  Unfortunately, passes that don’t lead to a made basket get lost in the black hole of basketball scorekeeping ignorance.  We don’t have any idea if threes are made more frequently if the shooter receives a pass as opposed to shooting off a pull-up J.  It’s a shame, really, because such information would be incredibly valuable for basketball research and analysis.

Well, thanks to 82games.com and their ultra-diligent charters, we no longer have to sit in the dark anymore.  A few years ago, they published a breakthrough study on their website that pulled the veil on good passing.  Rather than only focusing on made baskets, the team charted all shots and noted whether they were set up by a pass or not.  It’s a must read so go there and come back.  One of the several discoveries the 82 games team found in their charting was that non-assisted shots from close range are converted nearly 13 percent less than those that were set up by a pass.  Thirteen percent might not seem earth shattering but it is in the context of shooting.  Would you rather have Dwight Howard’s shooting percentage or Toney Douglas? That’s 13 percent.

Here’s the whole table from the outstanding study:

Interestingly, although most three-pointers are assisted (81 percent) according to 82games.com, the effect of a pass is smallest (+3.7 percent) compared to the others.  An assist on a close shot has over three times the impact.  In all, unassisted shots go went in .421 percent of the time whereas a pass propelled that figure up to .502 percent.   If you were wondering if passes really amount to anything, here’s your evidence.  All assists are not created equal.

These numbers take the macro view on the passing game and it would be foolish to assume that all players and shot types reflect the same percentage effects.  Certainly, there are personnel biases at play here and some particular point guards have no choice but to work within the confines of the offense sets.   Still, I wanted to apply these findings to the game’s best ball distributors and experiment how their assist total would change if we credited the assists according to each’s areas impact on FG%.  Last week, I asked how ball distributors get their assists with regard to high efficiency areas. This week, I’m asking a slightly different question: which players get their assists in shooting areas most impacted by the pass?

To get the quick and dirty measure, I set the average difference of 8.1% equal 1.  So an assist to a close shot receives a credit of 1.56 assists and likewise, a 3-point shot assist is credited 0.69 or ((3.7*1.5)/8.1) with the 1.5 adjusting for the bonus point.  Of course, there are several limitations to this exercise and should not be treated as an assist surrogate.  But it does shed more light about the assist variety.  Here’s the crop of the best in assists per game sorted by the difference in adjustment.

We find an interesting mix at the top.  Somewhat unexpectedly, Baron Davis paces the field and Mike Conley brushes shoulders with Deron Williams and Jason Kidd.  Why do they rank highly? By getting their assists in the areas most influenced by a set up pass.  Baron Davis feeds about 40 percent of his assists to chip shots around the rim which is far above than the average share.  On the other end, Jameer Nelson gives nearly 60 percent of his assists result to 3-pointers and dunks where the pass impact is generally low.

Note that New Orleans Hornets point guards Chris Paul and Darren Collison experience different effects after this adjustment.  Compared to his counterpart, Paul’s assists lead to a higher proportion of dunks to layups, which has pivotal implications on his differential.  I’m not sure how to coalesce the perceived immense value in Paul’s patented alley-oop floater with 82games.com’s dunk findings but I’d be willing to guess that a hybrid adjustment would be necessary.

Interestingly enough, the “impure” point guards gather at the bottom at the list.  Tyreke Evans, LeBron James, Kobe Bryant, and Dwyane Wade don’t receive a substantial upgrade by this measure because their dribble penetration play styles generate a high proportion of 3-point assists.  In fact, LeBron dishes out a 3-point assist nearly twice as often as his point guard Mo Williams.

Unfortunately, we’re limited to looking at these players using league average field goal percentage effects.  Admittedly, this a shortcoming that must be resolved before we get a complete picture of passers.  Some players cannot create their own shot off the dribble and have no choice but to get all three pointers from the catch-and-shoot (think Antawn Jamison).  They will undoubtedly experience varying passing effects than the norm.  Moreover, the component of foul shooting must be considered.  Read more about that in the 82games.com article.

In the end, if we get complacent and treat all assists the same, we’re missing out on the big picture of ball distributors.  We would benefit from rethinking the way assists are recorded and how we interpret those numbers in the box score.  With evidence to suggest close shots have are highly influenced by a pass, we can sharpen our approach in evaluating the impact of point guards and passing in general.  Hopefully after reading the last two articles, you’ll have a more complete understanding of the passing game and the drawbacks of the assist statistic design.  If anything, we must ask more questions and dig for more data to get at those elusive basketball truths that we seek.   I think I need an assistant.

Seth Carstens