A causal approach for detecting team-level momentum in NBA games

Abstract

This paper provides new evidence that team-level momentum exists in the National Basketball Association (NBA). The existence of momentum is one of the most prominent and longstanding questions in sports analytics. But for all its importance to announcers, coaches, and players, existing literature has found little evidence of momentum in professional basketball. This paper exploits a natural experiment in the flow of basketball games: television (TV) timeouts. Since TV timeouts occur at points exogenous to momentum, they enable the measurement of the effect of pauses in the game separate from the effect of strategy changes. We find TV timeouts cause an 11.2% decline in the number of points that the team with momentum subsequently scores. This effect is robust to the size of a run, substitutions, and game context. This result has far reaching implications in basketball strategy and the understanding of momentum in sports more broadly.