Adjusting for scorekeeper bias in NBA box scores

Abstract

Box score statistics in the National Basketball Association are used to measure and evaluate player performance. Some of these statistics are subjective in nature and since box score statistics are recorded by scorekeepers hired by the home team for each game, there exists potential for inconsistency and bias. These inconsistencies can have far reaching consequences, particularly with the rise in popularity of daily fantasy sports. Using box score data, we estimate models able to quantify both the bias and the generosity of each scorekeeper for two of the most subjective statistics: assists and blocks. We then use optical player tracking data for the 2015–2016 season to improve the assist model by including other contextual spatio-temporal variables such as time of possession, player locations, and distance traveled. From this model, we present results measuring the impact of the scorekeeper and of the other contextual variables on the probability of a pass being recorded as an assist. Results for adjusting season assist totals to remove scorekeeper influence are also presented.

Appendix: Availability of data

Sections 3 and 4 use ESPN box score data from the 2015–2016 NBA season. This data is publicly available and can be found at http://www.espn.com/nba/scoreboard. The SportVu optical player tracking data from STATS LLC used in Sect. 5 for the 2013–2014, 2014–2015, and 2015–2016 NBA seasons remains proprietary. However, to address concerns of reproducibility, our lab has released a full game of tracking data, available at https://github.com/dcervone/EPVDemo/blob/master/data/2013_11_01_MIA_BKN.csv.