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Posts Tagged ‘Rajon Rondo’

Besides scoring, the major contribution to a basketball offense is playmaking. Or, more specifically, the ability to draw extra defenders away from their assignments. As a measure of how well a player does this, assists leave something to be desired; they are only tallied when a pass is made to a player who scores, regardless of how helpful the pass was. Which is why we need a way to detect who creates open shots for teammates by drawing extra defensive pressure. For that, I use something I call “Opportunities Created.”

The Method

One way to do this is to track any time a second defender leaves his man in order to help defend an offensive player. This can be voluntary defensive strategy or it can be the result of the first defender being beaten off the dribble.

Such events are actually fairly easy to keep track of. Here’s a quick example from a game:

(Yes, I believe all NBA replays should be watched in Italian.) Note the first play of the video, when the ball is fed into Tim Duncan in the post. At about 0:21, help comes to double-team Duncan. This leaves Michael Finley open for a 3. The unguarded shot — regardless of the result — was created by Duncan drawing defensive help away from Finley. That is an opportunity created (OC) by Tim Duncan.

At 13:30 of the video, Dirk Nowitzki drives on Tim Duncan and forces Ginobili to help. The ball is swung around until Jerry Stackhouse ends up with a jumper (despite a nice close-out effort by Finley). That is also an OC by Nowitzki, who originally broke down the Spurs defense, despite it not registering as an assist.

Every OC has to end in some kind of attempt, even if it is a fouled attempt. If there is never a shot (or foul), there can never be an OC. (What exactly would the player have created, then?) OC’s can be registered when a player draws defensive pressure and the following occurs:

  • An open attempt
  • An open “hockey” attempt (extra passing, as in the Nowitzki play above)
  • A foul at the rim on a layup attempt (created by the scrambling of the defense)
  • An offensive rebound putback (created because the rebounder’s defender was forced to help)

The Results

As we would expect, guards create much more than bigs. They have the ball in their hands a lot, drive and dish a lot, and are often the defensive focus of pick and roll action. (It has become popular to “jump,” or trap the pick and roll to prevent the dribbling guard from penetrating or taking an open jump shot.) In last year’s playoffs, here is the positional breakdown of OC’s:

The breakdown by position is similar to data tracked this year as well.

So how well do assists correlate to OC’s? Overall, for the 133 players who logged at least 150 possessions in last year’s playoffs, the average error was 0.86 assists (with a standard deviation of 1.81 assists). Of those 133 qualifying players, the following had the largest discrepancy between assists and OC’s per 100 possesions (number of OC’s per 100 in parentheses):

  1. Rajon Rondo 6.8 (5.6 OC’s per 100)
  2. Ronny Price 5.8 (1.2 OC’s)
  3. Jason Kidd 4.7 (4.7 OC’s)
  4. Luke Walton 4.0 (4.0 OC’s)
  5. Jamrio Moon 3.9 (0.0 OC’s)

and the following players have the largest discrepancy between OC’s and assists (meaning they create more than assists would suggest):

  1. Brandon Roy 5.3 (8.7 OC’s)
  2. Nowitzki 4.0 (8.3 OC’s)
  3. Ginobili 3.3 (12.4 OC’s)
  4. Westbrook 2.8 (11.7 OC’s)
  5. Reddick 2.4 (6.3 OC’s)

I will post the complete leaders from last year’s playoffs in a follow up post.

The Discussion

There is a fairly strong correlation with assists (R=0.83). However, the error rate in certain players is enormous, which was the impetus for the stat in the first place; we want to know who’s creating opportunities, not simply who is passing to good players.

It might be worthwhile to simply track double-teams, but there isn’t always an attempt of some kind after a double team. Sometimes, the ball is re-entered into the post and a second or third double team can come on the same possession. If the player turns the ball over, nothing positive came from the double team.

Future consideration should be given to the defensive version of this metric: “OC’s Against.” Those occur every time a defender has a teammate help him in his assignment. If a player never needs defensive help, it means that he is never responsible for the offensive “power plays” (4 on 3 on the rest of the court) that occur because of an OC.

Another useful follow up exercise would be to look for “ball-stoppers.” Most NBA players and teams are coached well enough to take advantage of the power play provided  when two defenders commit to one offensive player. Every once in a while, a player will allow the defense to recover and lose that advantage by holding the ball or not shooting when he should shoot, allowing a scrambling defense to recover. It’s fairly easy to spot, and seems worth tracking in the future.

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One common trend in basketball discussions is the misuse of statistics. Since most people lack any formal education in statistics, and since humans fall prey to all sorts of statistical phenomena — Gambler’s Fallacy, for example — it never hurts to reiterate that statistics only capture what they are trying to capture. Nothing more, nothing less.

So how should we interpret the box score in basketball?

The first thing to remember is that basketball is a game of possessions. Adjusting for pace and minutes played is important in normalizing statistics. We want to compare numbers on a level playing field. Without normalizing, comparing raw statistics would be like comparing the speed of two runners in kilometers/hr versus miles/hr, or the averages of an NBA player after halftime versus per game.

Playing more minutes/possessions is indeed meaningful, but not that meaningful. While it’s better to have a star on the court for 90% of the game than 80% of the game, remember that fatigue is an issue and that in some situations, 2 mpg can be explained away simply because one player sat during garbage time of more blowouts.

Furthermore, if two players are both 10 points better per 100 possessions than their backups, the 2 mpg difference will result in a 0.25 increase in team efficiency at today’s pace (~93 possessions per game). In other words, with two superstars of the same value with the same quality backup, one would need to play eight minutes more per game to raise his team’s efficiency by a single point.

As for the specific figures from the box:

Points

Points are not the be-all end-all that some make them out to be, but more importantly they aren’t even a true measure of “scoring ability.” They are, actually, just a measure of points. A number of variables go into a player scoring a basket, primarily who his teammates are and how successful the opposing defense is in defending him.

Think of the multitude of ways to score that don’t represent the same skill set or level of difficulty:

  • Making a contested perimeter jumper off the dribble
  • Scoring in the post against a double team
  • Driving by one’s man — with or without a screen — and finishing at the rim

All of these are ways individuals create offense. They don’t really have the help of their teammates. But then again, sometimes the above actions don’t result in scores, and we see players:

  • Shooting open jumpers or 3-pointers
  • Scoring on an uncontested putback
  • Getting an open layup or dunk

These three situations were assisted by the creation of other people’s offense. The creator drives and kicks to the open shooter because the defense had to sag. The offensive rebounder is suddenly alone because his man went to double a post threat. And if someone gets to play with a great creator who draws defensive attention, sometimes just by magically running to the hoop he will have an open layup or dunk.

Knowing how people generate their shot attempts (and subsequent points) is important in understanding them. Which leads us to…

FGA’s and True Shooting%

Points can’t be properly interpreted in a vacuum. A 30 point game isn’t too sexy if a player took 40 shots to get there. (However it might be more understandable if the player’s teammates shoot poorly as well and are unable to generate any offense. Both of these apply to understanding Allen Iverson’s statistics in Philadelphia.)

It’s standard to evaluate volume (FGA’s) in conjunction with efficiency (TS%), the thinking being that generating more good shot attempts is challenging and we should expect to see a corresponding dip in efficiency. Similarly, we would not expect a player shooting six times a game at high efficiency to maintain his shooting percentage if he were suddenly asked to generate more shots outside of the easy layups his teammates creates for him.

Rebounds

Rebounding % is the best statistic here, although it’s not in the box. Once we adjust for pace or calculate rebound % (an estimate of the rebounds of the total number of available misses in a game), one of the more difficult tasks is to determine impact rebounding. That is, who’s rebounding is truly helping their team more.

Taking boards from teammates instead of from the opposition isn’t terribly helpful. If all six of a guards rebounds are from misses that his teammates were in a position to grab, then his rebounding isn’t helping much. Then again, if all six of his rebounds were boards that the opponent otherwise would have grabbed, he’s contributing quite a bit to the differential. Measuring this is a difficult task.

The final note about rebounds is that positional adjustments and scheme are important to know. This matters quite a bit, as we want players under the hoop to grab more rebounds than players on the perimeter. And if teams don’t crash the glass on offense, we need to account for that in comparing offensive rebounding numbers to teams who do.

Assists

One of my least favorite stats. Ideally, we want to understand who creates more offense for teammates. Assists can often be simply passing the ball to a great shooter, a great scorer, or feeding a great post player. These passes border on rudimentary and can result in huge assist totals despite doing very little.

However, assists do a decent job of approximating creation. Some players have examples that swing one way or another. Rajon Rondo has huge assist numbers this season, but many of those are from making the “correct pass” versus creating for teammates. The creators often have many “hockey assists” from the extra passes that their double team draw, and as a result are creating more offense that their assist total would suggest.

Opposite of Rondo, we have someone like Deron Williams, creating more than the numbers would suggest. In last year’s playoffs, Williams tallied 12% more assists/75 possessions than Rondo and had a 2% higher assist rate. However based on my tracking, he created 248% more offense for his teammates than Rondo!

Turnovers

An important stat. Turnovers are worse than missed shots for two reasons: there is no available offensive rebounding opportunity (which results in a second chance 26% of the time) and turnovers often lead to decreased defensive efficiency because of the resulting fast breaks for opponents.

It’s important to know an individual’s role here again. We would expect more turnovers from someone who has the ball more. Turnover % attempts to capture this, and it’s a pretty good estimator from what I can gather.

Steals

Another good stat. These are almost the inverse of turnovers, because we know the defender pilfered a possession from the opposition and likely led to an odd-man break for his team. Steals are not a measure of being a good defender, as sometimes players cheat a lot or reach a lot to generate steals, and there is no current statistic for the number of times they are burned on failed steal attempts.

But steals are important and they are generally well-tracked. For instance, forcing a jump and winning it counts as a steal. Although there are times deflections for turnovers are missed.

Other

Blocks is the final major stat in the box, but I find them somewhat deceiving. For bigs, blocks are, yes, just a measure of blocks. It’s a moderate estimate of that player’s presence at the rim (usually), but it’s not an indicator that someone is a defensive superstar. Tim Duncan has never finished higher than 3rd in blocks per game, but he certainly was the best post defender in the NBA on more than one occasion. For perimeter players, a small boost in blocks can often indicate some defensive prowess, but again, it’s not a major stat for determining great defensive play, and there isn’t too much inherent value in a block to begin with.

I will probably follow up with another post on some of the advanced statistics and how to treat +/- numbers. But the final piece of the puzzle is always glancing at the team’s stats and using them as context. How good is a team’s offensive or defensive rating? How well do they rebound? How many other scorers do they have? All of these must be factored in when understanding a player’s contributions. More on this later.

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