This is the first real-world study to examine the association between a voluntary 16-ounce (oz) portion-size cap on sugar-sweetened beverages (SSB) at a sporting arena on volume of SSBs and food calories purchased and consumed during basketball games. Cross-sectional survey data from adults exiting a Brooklyn, NY, USA arena (Barclays, n = 464) with a 16-oz portion-size restriction and a Manhattan, NY, USA arena with no portion-size restriction (Madison Square Garden, control, n = 295) after the portion cap policy was put in place from March through June 2014 were analyzed. Linear regression models adjusting for sex, age, BMI, ethnicity, race, marital status, education, and income were used to compare the two arenas during the post-implementation period. The survey response rate was 45.9% and equivalent between venues. Among all arena goers, participants at Barclays purchased significantly fewer SSB oz (-2.24 oz, 95% CI [-3.95, -0.53], p = .010) and consumed significantly fewer SSB oz (-2.34 oz, 95% CI[-4.01, -0.68], p = .006) compared with MSG after adjusting for covariates. Among those buying at least one SSB, Barclays' participants purchased on average 11.03 fewer SSB oz. (95% CI = [4.86, 17.21], p < .001) and consumed 12.10 fewer SSB oz (95% CI = [5.78, 18.42], p < .001). There were no statistically significant differences between arenas in food calories and event satisfaction. In addition, no one reported not ordering a drink due to small size. An SSB portion-size cap was associated with purchasing and consuming fewer SSB oz. without evidence of decreasing satisfaction with the event experience.