The basic numbers for teams

If we want to analyze statistics without things being skewed due to tempo--and we do--then what we need to look at is something called "tempo-free" or "possession-based" stats.

The main point is, we don't particularly care how many points per game a team averages, because PPG is dependent more on pace than on efficiency.

What we want to know is how effectively a team uses their possessions. Thus we are interested in stats like "points scored per possession" and "points allowed per possession."

But such stats are not published. In particular, "number of possessions" is not published. This is a problem, because we don't want to have to watch every single game to calculate them.

Luckily for us, basketball guru Dean Oliver developed a way of calculating number of possessions just from the box score. Ken Pomeroy has pulled Oliver's ideas into college hoops and built upon them. We borrow them.

The idea is to ask oneself in what way a team's possessions can end. And the answers one comes to are, (1) by a shot that isn't rebounded, and (2) by a turnover.

There is one difficulty: free throws. Sometimes one free throw ends a possession (if the front end of a one-and-one is missed); sometimes two free throws end a possession; and sometimes a free throw ends a possession that we already counted (if a player is fouled while making the FG). Ken Pomeroy actually watched a large sample of games, and determined that in college ball, about 47.5% of free throws end a possession. So that's the number we'll use. Our formula (therefore) is:

Possessions = FGA - OR + .475*(FTA) + TO

Now that we have possessions, we want to know what our individuals and teams are DOING with these possessions. The most obvious things they could be doing are scoring, missing shots, and turning the ball over. So we'll start with those.

We already have a couple of good stats for measuring missed shots (eFG and PPWS), so let's go on to scoring.

Team scoring is easy. We just ask how well a team converts possessions into points! We call the stat "offensive efficiency" (Oeff):

Oeff = Points/Possession

Likewise we can measure defensive efficiency--how well a team prevents the other team from converting possessions into points.

Deff = (Points allowed)/(opponents' possessions)

Since possessions are measured by means of shots, offensive rebounds, free-throws, and turnovers, we can break down a team's offensive (or defensive) efficiency by taking a closer look at these four categories. We call them the "Four Factors." The first is effective field goal percentage, which we've already looked at. The others are turnover rate (TO-r), offensive rebound rate (OR-r), and free-throw rate (FT-r).

TO-r just tells us what percentage of possessions end in turnovers:

TO-r = 100*(TO)/Possessions

OR-r tells us how well a team keeps its possessions alive by rebounding its own misses. But be careful--we don't want offensive rebounds per game, or even per possession. What we want to know is what percentage of our own missed shots we pull down. We set

OR-r = 100*(Team OR)/(Team OR + Opponent DR)

Finally, we want to know how often we get to the free-throw line, and make free-throws. We could take this as a fraction of possessions if we wanted, but the standard stat is to take free-throws as a percentage of field goal attempts:

FT-r = 100*(FT/FGA)

We just reverse all of the above team stats with opponent stats to analyze a team's defense, with one exception: we can't control how well our opponents shoot free-throws, so we use free-throw attempts instead for analyzing a team's defense:

FTA-r = 100*(FTA/FGA)