New Hoops Stats 101

Here at FB&G we use a lot of the new, “moneyball” NBA statistics. The reason is pretty simple, I think they do a better job explaining what we see on the court than traditional statistics. But if this is all new to you, here is a little primer.

Let’s start with the most basic of questions: What wins basketball games? Obviously, scoring more points than your opponents — it’s been that way since the day James Naismith nailed up the peach baskets. However, by the basic rules of basketball, you and your opponents will have the same number of possessions per game, so what really is the key is being more efficient in your possessions than your opponent.

The best way to compare offenses and defenses is on a level playing field, meaning in points scored per possession. To make that a more easily digestible number, we talk about points scored/given up per 100 possessions (which is slightly more than in the average NBA game). We call that number offensive/defensive rating. For example, if for each 100 possessions the Lakers are averaging 105.4 points, that is their offensive rating. If they are giving up 102.9 points per 100 possessions to their opponents, then they would be a slightly better than .500 team.

Points per possession is a better barometer of a team than points scored per game because the latter is influenced by the pace games are played at (pace can be measured separately).

The next logical question is what factors lead to scoring on a possession? And, its corollary question, what can be done to stop an opponent from scoring?

Dean Oliver, in his groundbreaking book Basketball on Paper, says there are really only four ways to create offense on the team level: shoot accurately, don’t turn the ball over, grab offensive rebounds, and get to the free throw line. These things are often called “the four factors.” These things are not equal — shooting efficiency is twice as important and limiting turnovers and getting offensive rebounds. Getting to the free throw line is the least important.

How well you defend those four areas gives a good picture of a team’s defense.

Some people will ask if these statistics are valid. I’d obviously answer yes. In the same way that baseball statistics are valid because of the number of trials (a starting major leaguer gets more than 500 at bats per season, for example) basketball stats are also valid. There are 82 games a season and that means most teams have upwards of 7,400 offensive possessions per season. A star player like Kobe Bryant may take upwards of 1,100 shot per season but even a role player will take hundreds (381). The volume is there to make valid analysis.

One stat we use around here is John Hollinger’s PER, or Player Efficiency Rating. It is not the end all/be all of a stat, but it is a nice snapshot. I’ll let Hollinger explain PER (from his site):

The formula, which I call the Player Efficiency Rating (PER), adds the good (made shots, steals, assists, rebounds, blocked shots, free throws), and subtracts the bad (missed shots, turnovers, fouls) by assigning a point value to each item (I arrive at the point values in a fairly tortuous way, and that’s one of the parts I’m saving for the book). The rating for each player is then adjusted to a per-minute basis (so that, for example, you can compare subs with starters in the frequent ‘he should start ahead of so-and-so’ debates), and also adjusted for the team’s pace. In the end, one number sums up the players’ accomplishments (the statistical ones, anyway) for that season. I’ve set it up so that the league average, every season, is 15.00, which produces sort of a handy reference guide:

A Year For the Ages: 35.0
Runaway MVP Candidate: 30.0
Strong MVP Candidate: 27.5
Weak MVP Candidate: 25.0
Bona fide All-Star: 22.5
Borderline All-Star: 20.0
Solid 2nd option: 18.0
3rd Banana: 16.5
Pretty good player: 15.0
In the rotation: 13.0
Scrounging for minutes: 11.0
Definitely renting: 9.0
On next plane to Yakima: 5.0

Over at the site, they produce an oPER or Opponents Player Efficiency Ratings. This is the same as PER, but done to whomever a player is guarding to give you an idea of the defensive performance of a player. This is a flawed system when applied to one player because of zone coverages, switch offs and the rest of the way defense is played in the NBA. However, oPER it works pretty well when applied to a position. For example, if the Lakers are allowing an oPER of 10.9 against opponents shooting guards, well below the league average of 15, then they defend that spot well. However, they are getting burned at the three, say an oPER of 18.9, then we have a problem.

Other stats seen around these parts.

eFG% or Effective Field Goal Percentage. The problem with basic/traditional field goal percentage, particularly when talking about guards, is that it counts a made three-pointer the same as a made two pointer — the equivalent of a football stat that counted touchdowns and field goals as the same. Clearly those are not worth the same amount, and neither is a two-pointer and a three-pointer in basketball — a three-pointer is worth 50% more on the scoreboard. So eFG% gives players that bonus (50%) for making the more difficult shot (the equation can be seen as eFG% = (2PM + 1.5*3PM) / FGA or eFG% = (FGM + 3PM/2)/FGA).

+/- Numbers. One of the best gauges of a player’s worth to a specific team comes from looking at the difference in how the team plays with the player on court versus performance with the player off court. The on court +/- number represents the team’s net points with the player on the floor per 48 minutes, while the off court number is the team’s net with the player off the floor per 48 minutes.

There’s a lot more information on basketball statistics out there Check out places like 82games, or Knickerblogger on the Web.