0393 Free Throws Aren’t Free: The Cost of Daylight-Saving Transition in the NBA

Abstract Introduction Daylight Saving Time (DST) affects more than 1.5 people globally and produces both circadian misalignment and acute sleep loss, particularly during the spring transition. Both mechanisms can impair athletic performance, particularly skill-based tasks like shooting free throws in basketball. Prior work has documented adverse health and safety outcomes surrounding DST shifts and has been shown to be associated with performance decrements in endurance running events. Whether DST transitions impact skill based athletic performance remains unclear. This study evaluated the impact of spring and fall DLS transitions on National Basketball Association (NBA) free-throw percentage (FTP). Methods Using a natural-experiment design, we analyzed regular-season NBA games across 29 seasons. Individual athlete’s free-throw makes and attempts were extracted from ESPN play-by-play data and matched to DST calendar dates. Arizona games on DST days were excluded. For each season, DST-day FTP was compared with two same-season baselines: (1) the week prior and (2) the entire non-DST season. Analyses were performed at league, team, and individual levels. Players were grouped into tertiles by baseline FTP, and quality-filtered analyses required ≥3 attempts in both windows. Paired samples t-tests evaluated mean FTP differences (ΔFTP). Bonferroni correction-controlled multiplicity for six primary week-prior comparisons. Exploratory analyses evaluated post-DST Days +1 to +3 and correlations between ΔFTP and prior-day time-zone travel. Results Across 34,316 player–game observations (>1.5 million free-throw attempts), no significant DST effect was detected at the league or team level for either transition. The only decrement surviving multiplicity correction occurred in the spring among players in the highest baseline-FTP tertile: league-level ΔFTP = −0.025 (p = 0.0039) and individual-level ΔFTP = −0.031 (p = 0.0009; ≥3-attempt filter). No other spring or fall tertile reached significance after correction. Exploratory post-DST and time-zone-travel analyses produced small, inconsistent estimates with no reproducible patterns. Conclusion A modest decline in FTP after the transition to spring DLS was observed only among the highest-accuracy shooters. Whereas DLS transitions do not meaningfully impact free throw percentage at the league or team level, nor in those starting from a worse baseline FTP. Overall, the findings indicate minimal performance impact of DST on professional basketball free-throw shooting. Support (if any)