The NBA was against legalized sports betting until Silver took over:
"For years, former National Basketball Association Commissioner David Stern believed being associated with gambling would hurt the integrity of professional sports.He even testified on behalf of NBA star-turned-senator Bill Bradley’s Professional and Amateur Sports Protection Act (PASPA), which became law in 1992 and prevented sports wagering from expanding beyond four states that already had some version of it, including Nevada, the only state with legal race and sports books."
After he left the NBA he changed his mind but I believe all of the other sports have campaigned against it for many years