The USAC officials at the race should be able to make a judgment call as to whether or not the handups from the spectators are having a negative effect on the race/racers. If they are, then they need to talk to the promoter and tell them to do something about it or actions will be taken.
The way it stands now, USAC is trending towards making cross events less fun, and making it something different than what has made it so popular.
I think the NFL turning into the No Fun League is the right analogy.