Four Factors

At the most basic level, teams win basketball games by scoring more points than their opponents. But how do they go about doing that with the many skills needed for basketball? In 2004, Dean Oliver expanded upon his “Four Factors” philosophy from his 2002 book, Basketball on Paper, in an attempt to identify how four important strategies relate to success in basketball. The novelty of understanding these factors appear in the way of analytic development in an effort to shed light on emphasis of each factor.

The four factors are to score efficiently, protect the basketball on offense, grab as many rebounds as possible, and get to the foul line as often as possible. Each of these elements is closely related to the termination of a possession for a team. There are other options such as dead ball rebounds, end of period, and specialized fouling situations. These are few and far between and rarely impact possession data over the course of a season. Hence the focus is on the main four ways to terminate a possession.

Score Every Possession

This rule is the simplest of all and tends to be one of the hardest. An ideal team will always score, every time. However, teams are never ideal and we are left with attempting to identify the best way to measure scoring in the NBA.

Oliver proposed using effective Field Goal Percentage (eFG%). This measure is a scale corrected measure to identify field goal percentage for a team. The scale correction is to account for three point field goals. Note, however, eFG% cannot be taken alone. For instance, you cannot determine the type of team (block vs. perimeter) with eFG% alone. However, with eFG% we do obtain the best relative measurement for points per field goal attempt; simple by multiplying by two.

The easiest way to calculate this is: (FGM + .5*3PM)/FGA.

Pick Up All Rebounds

If a team cannot score on every possession, then the optimal task is to grab every miss and give the team a second-chance opportunity. An offensive rebound extends a possession and allows for a second attempt at a field goal. This is effectively a “do-over” for teams and when strategized around properly, can be a deadly plan of attack for a team.

To measure the quality of a team’s ability to rebound, we simply compute the offensive rebounding percentage (OREB%). This quantity is calculated as the number of offensive rebounds divided by the number of available rebounds after a missed field goal attempt. This value is not over the number of missed field goal attempts.

These are measured by:

• OReb% = TmOReb / (TmOReb + OppDReb);
• DReb% = TmDReb/ (TmDReb + OppOReb).

The Toronto Raptors in the 2017 NBA season managed 871 offensive rebounds while giving up 2,619 defensive rebounds. Despite this, the Raptors missed 3,707 field goal attempts. This leaves 217 missed field goal attempts out of the picture. These can be attributed to dead ball rebounds, fouls before a rebound is secured, and expiration of period.

Whichever reason, this is why we do not divide by the number of field goal misses. For the Raptors, their OREB% for the 2017 season is 0.24957.

Get to the Foul Line

The next way to score points other than scoring a field goal or giving the team a second opportunity is to get to the foul line. Getting to the foul line serves two purposes in a game. First, it guarantees attempts to score points. Second, it inches opponents ever closer to being out of the game. Just getting to the line is not enough. Converting said attempts into points becomes the most important part of the equation.

To measure a team’s quality of getting to the foul line is to identify the number of free throws made per field goal attempt, called the free throw rate (FTRate). The reason the comparison is to FGA instead of Number of Possessions is unknown. However, it’s not absurd. This is due to the fact that most teams average just under a field goal attempt per possession. For the 2017 NBA season, the worst team was the Brooklyn Nets (0.8401) while the best team was the Detroit Pistons (0.9414).

Protect the Basketball

The final step of the four factors is to ensure that, other than a defensive rebound, a field goal attempt or free throw attempt terminates the possession. That is, don’t turn the ball over. This is a simple measurement called turnover percentage (TO%). This measure is simply to calculate the percentage of possessions that ended in a turnover. That means the formula is TO/(FGA + (.44*FTA) – OR + TO).