Scoring Contribution Percentage

An Alternative Metric to True Shooting Percentage

Damon Smith

June 27, 2013

“What these young bloods have to understand is that this game has always been and will always be about buckets.” – Bill Russell to Uncle Drew

Introduction

There’s a good bit of truth in 11-time NBA Champion Bill Russell’s comment during the Pepsi MAX “Uncle Drew” commercial. Winning basketball is defined by outscoring the opponent, and that requires both maximizing and optimizing a team’s possessions. Simply put, there are only two ways to score more points in a game: (1) score more points per possession, and (2) create extra possessions. True Shooting % is a good indicator of the first measure, since it takes into account the value differentials associated with a successful scoring possession. The basic concept is that a 3-point field goal made is 50% more valuable than a 2-point field goal attempt, even as both attempts “cost” the team exactly one possession. As such, True Shooting % can

be used to comprehensively represent shooting efficiency by combining a team’s field goal %, 3-point field goal % and free throw % into a single metric.

The formula for calculating True Shooting % is as follows:

TS% = PTS/(2x(FGA+0.44*FTA))

where:

PTS = points

FGA = field goal attempts

FTA = free throw attempts

“The .44 multiplier is because not all free throws take up a possession. Technical foul shots and ‘and-ones’ do not, while there are more than two free throws on one possession with a three-shot foul. Research has determined that about 44% of all free throws take up possessions, thus .44 is used as the multiplier.”1

Methodology

Scoring Contribution % is simply True Shooting % adjusted for extra possessions created by offensive rebounds, steals and blocked shots and for possessions lost from turnovers.

The formula for calculating Scoring Contribution % is as follows:

SC% = PTS/(2x(FGA+0.44*FTA)-OR-S-(0.57xB)+TO)

where:

OR = offensive rebounds

S = steals

B = blocked shots

TO = turnovers

Scoring Contribution % = True Shooting Percentage adjusted for extra/lost possessions. The .57 multiplier is applied to blocked shots because 57% of blocks result in a change of possession.2

1 “Statistical Analysis Primer”. Nba.com. 2007.2 “A Study of the Value of Blocked Shots”. 82games.com. 2003.

Analysis

This analysis compares the relative merits of Scoring Contribution % and True Shooting % as they pertain to indicating both the winner of a game and the scoring differential of the two teams. For this analysis, I used the 2013 NBA Playoffs as my sample (85 total games).

Scoring Contribution % is more closely correlated to Playoff Wins than True Shooting %.

Figure 1:

When the variance in Scoring Contribution % between two teams was >1%, the team with the higher Scoring Contribution % won 79 of 79 games (100%).

When the variance in True Shooting % between two teams was >1%, the team with the higher True Shooting % won 69 of 79 games (87%).

These findings are statistically significant when applying a 95% confidence interval (Figure 1).

Scoring Contribution % is more predictive of Playoff Scoring Differential than True Shooting %.

Figure 2:

In this analysis, the coefficient of determination (RSquare) measures the proportion of variability in the dependent variable (scoring differential) accounted for by the model.

The results indicate that 69% of the variability in scoring differential is explained by Scoring Contribution %, whereas only 35% of the variability in scoring differential is explained by True Shooting % (Figure 2). This analysis is based on all 85 2013 NBA Playoff games.

Conclusion

In this analysis, I have introduced a new basketball metric, Scoring Contribution %, which is derived from True Shooting % and adjusted for extra possessions created by offensive rebounds, steals and blocked shots and for possessions lost from turnovers. I have demonstrated that Scoring Contribution % is a superior metric to True Shooting % in identifying the winner of an NBA game, as well as predicting the scoring differential. Applied at an individual player level, Scoring Contribution % could be useful in evaluating the overall offensive efficiency of players; however, other variables, such as player position, would need to be controlled for relative comparisons.