One of the great examples of 'feedback' in Celtics history - though it didn't involve a player. On John Havlicek Appreciation Night near the end of his last season, Irv Levin, then the Celtics owner, was announced to present Havlicek with a gift. Levin was booed mercilessly by the Garden fans, and it totally shocked him. They booed him because he had run the franchise into the ground. It was reported afterward, that the booing he got that night helped convince Levin to sell the team - which ultimately led to the infamous franchise swap with Buffalo that ushered in the John Y. Brown era.
So unfortunately, things got worse before they got better, but the feedback from the Garden fans that night helped get rid of an owner.
Booing can have an effect....