Friday, February 22, 2013

Hedge Against the Machine: How to Limit the Spurs’ Offense


As the Clippers were handed a decisive 26-point home loss by the Spurs Thursday night, TNT's Reggie Miller and Chris Webber referred to the Spurs' offense as a “machine.” Every player knows where he needs to be, what pass to make, and which open shot to take (yeah, a lot of times they have many in the same possession).

A lot of credit for the Spurs' offense is given to “best point guard in the NBA right now,” Tony Parker, who went for 31 points, 7 assists, and a game high +31 plus/minus on Thursday night. But the key to the machine is clicking on all cylinders: The Spurs' effective use of on- ball screens in the halfcourt.

Using the Vantage data set, we can see how the Spurs’ use of on-ball screens leads to "effective outcomes" (i.e., scores, assists, open shots, passes to open shots, passes to shooting fouls, and shooting fouls).  On the flip side, we also see that when defending against on-ball screens, a more aggressive initial screen defense can limit the dribble penetration of the screen receiver as well as scoring opportunities from role players.

On-ball screens are a major part of the Spurs' production. To start, the screen quality of Spurs' on-ball screens is among the best in the NBA -- Spurs' on-ball screens make contact with or reroute defenders 50.75% of the time (2nd only to Detroit).  Out of the 24.33% of Spurs' on-ball screens that lead to effective outcomes, nearly 15% of those plays are passes to missed open shots, which leads all NBA teams in the Vantage data set.  But the Spurs are top in the league in offensive efficiency.  These stats show how crucial it is for the Spurs' machine to be working together.  The fact that the Spurs are missing a high percentage of open shots in screen situations and yet still are among the best in the league in scoring in these situations illustrates that their efficiency isn't driven by raw scoring prowess but rather by generating so many good looks that they more than make up for their misses.

Tony Parker’s use of on-ball screens aids him in his ability to facilitate the offense. Of the on-ball screens he receives, 81.88% involve not splitting the screen and not refusing the screen, another example of the structured nature of the San Antonio offense. Overall, Parker will pass coming off a no-split, on-ball screen nearly 75% of the time. Out of those screens, Parker generates an effective outcome (assist, crucial pass, pass to open shot, pass to shooting foul) 34.02% of the time. This suggests that a way to limit Parker’s ability to penetrate and find open shooters is to limit his actions when he comes off the screen. Pressuring Parker and forcing him to retreat (which our data set shows he is forced to do only about 8.24% of the time) would help in limiting his ability to feed the machine.

With 59.44% of all of Parker’s on-ball screens received coming from the high post or 2-point wings, an initial screen defense that hedges against on-ball screens may have the most success when defending these court locations. Sampling the entire data set, we can see that hard-show screen defenses lead to ineffective or nonsignificant outcomes 64.1% of the time, as opposed to soft-show and drop-zone defenses, which yield to ineffective or nonsignificant outcomes 61% and 57.39% of the time, respectively. Although hedging can be a more aggressive initial on-ball screen defense, especially against a quick player such as Parker, statistically it allows the fewest field goal attempts against and scores by a player the defender isn’t guarding. Although it may give up the fewest field goal attempts, it gives up the highest field goal percentage (44.96% compared to more frequently used initial screen defenses, playing behind or showing, which give up 38.91% and 34.31%, respectively). The reward with hedging, however, is that the recovery rates are a lot higher, as 70.9% of hedges lead to recovery on secondary screen defense (compared to 61.9% and 58% for drop zone and soft show, respectively).  Thus, the hard hedge allows the defending guard to recover as the primary defender, which limits dribble penetration.  

Ultimately, one way to stop the Spurs is to not allow all of the moving parts of the machine to function according to plan. Through Parker’s facilitation, which has been especially noticeable this season (6th in the league in assists), it has helped guys such as Matt Bonner and Kawhi Leonard gain All Star weekend recognition as the benefactors of the high-powered offense. Limiting the offense through aggressive screen defense puts more pressure on the ball-handler, while limiting role players’ presence in San Antonio’s offensive schemes. 

Tuesday, February 12, 2013

Does Greivis Have a Grievance?


Is it a snub if the NBA leader in assists is not going to the All-Star Game? Ask third-year Hornets point guard Greivis Vasquez, who has been piecing together the best season of his young career and emerged as one of the league’s best facilitators.  In a season that was destined to feature two of the brightest stars from this year’s rookie class, Anthony Davis and Austin Rivers, it’s been Vasquez’s statistical production that has stood out.  But is it too early to compare him to the NBA’s current All-Star point guards?

Good Indirect Facilitator

As discussed here before, we can find ways to measure Vasquez’s facilitating production even in cases that don't result in a box score assist. The Assist+ Ratio is the number of assists to combined crucial passes (i.e., the hockey assist), passes to missed open shots, and passes to shooting fouls, thereby taking the finishing abilities of teammates out of the equation (lower ratio meaning less help from teammates).  The Assist+ to Crucial Passes Ratio is a measure of indirect facilitation (lower ratio meaning more indirect facilitation compared with direct facilitation).  The following chart compares the top seven NBA assist leaders as of February 10, five of whom are 2013 All Stars, using the Vantage data set:

Rockets coach Kevin McHale knows Vasquez’s improvement has helped develop the Hornets’ young offense, saying, “He’s got to be in the top 10 (in the NBA) as far as importance to his team, when you look at the percentage of points he produces either scoring or assisting on or being involved in a play” (emphasis added). The data support McHale’s theory, as Vasquez is third, and in a group that is significantly ahead of the rest, in our indirect facilitation metric.  This suggests that Vasquez moves the ball well in finding his teammates and creates plays even if he's not getting credit in the box score.  The Assist+ Ratio has Vasquez is in the middle of the pack among the NBA assist leaders, which bodes well for his team's young scoring core.

Smart Passer

Another upside to Vasquez as a facilitator is his ability to make smart decisions. Out of our group of seven, Vasquez is second only to Rondo (by 0.002%) in deflected pass percentage, which measures the number of passes deflected divided by total passes made. Looking at turnovers, we can see Vasquez’s ability to avoid turnovers in making his passes. As a general rule, bad pass is the most frequent turnover type for point guards.  Out of the seven assist leaders, Vasquez has the third lowest percentage of turnovers due to bad passes. 
To measure Vasquez’s ability to avoid bad passes in situations where an assist might be attempted, we are able to look at his percentage of turnovers that he commits after his feet have left the ground.  These are usually instances where the point guard decides to make a play that isn’t a shot attempt. Our data show that Vasquez is the best of the group in terms of not turning over the ball while in the air.
There is, however, another way to look at these numbers given the correlation of percentage of in-air turnovers to points per game.  Perhaps Vasquez isn't being as aggressive as he could be in scoring.  There is such a thing as being too good at a stat if it suggests you're not taking enough risks thereby limiting your potential rewards.  In the last part of the season, as the Hornets Pelicans look toward next season, the numbers suggest that Greivis could and should try to penetrate more to create more offensive production.

Areas to Improve

Along with Vasquez’s high assist numbers, there are also high turnover numbers that have come with it. Vasquez has the fifth most turnovers in the NBA, but despite that, he still better than Holiday and Westbrook, who are second and fourth, respectively.  Looking at the forced/unforced turnover ratio (see chart below), Vasquez’s turnovers are more often the result of his forcing the matter rather than mistakes made by his teammates. But, as we saw above, his bad passes do not comprise the majority of his turnovers.  Vasquez’s high turnover numbers are representative of his ball-handling as opposed to his passing.  Where he has struggled most is on lost balls off the dribble and other ball-handling errors, which combined almost equal his bad passes.  The other elite guards are nowhere near this in their turnover numbers.
While Vasquez’s ASS/TO ratio so far this season ranks behind Paul, Parker, and Rondo, for each of these players, we saw an increase in production from their first three seasons.  Likewise, Vasquez has increased steadily during his first three seasons: 2.2, 2.4, and 2.8 (as of 2/10/13).
One notable difference in Vasquez’s game is that he's not quite the scoring threat as the other names on the list.  Vasquez is also different from these point guards in that he is used the least frequently in perimeter isolation plays.  As we saw above, his ball handling needs some work, as does his risk-taking on scoring opportunities, but if he can make the jump to be a little more aggressive and confident, there is room for him to grow into more of an offensive threat in both facilitating and scoring.

Which leaves us with our original question: Is Vasquez being dis'ed by not getting selected as an All Star? Our data show that while Vasquez is indeed an elite passer, he's got some work to do on the scoring side. With five of the seven names mentioned here going to Houston this weekend, it goes to show that in today's NBA, there is more to a point guard than being a good passer.