There are probably a few of us on this forum who can remember those days in the 60's when the crowd and players were expected to be absolutely still and quiet when a high school or college basketball player was shooting a free throw. Then it seemed there would always be one jerk who would shout or move at the time of the shot. Then everybody said f%%k it, they shoot harder shots during the game with the crowd going wild, why can't they shoot an undefended free throw? And now, the crowd can't make enough noise, yet the free throws still go in.
I don’t know if this has been tested, but my belief is that sudden movement or sound in a quiet and still environment is way more distracting than a lot of constant movement and sound. So if I wanted to distract a basketball player shooting a free throw, I would have everyone sit still and then have one fan suddenly move and shout as they are shooting.
That accords with my own experience in the pool hall. A bunch of people walking in the distance is easier to fade than sudden movement in a still environment as I’m shooting.