The verdict: the story is that Roberts, through the roof hatch of his motorhome, took a 22 rifle and shot down a Bib balloon at Loudon. This is said to have happened in the early 1970s before the start of the Loudon national. Roberts used Goodyear tires, you see. 

The AMA and the owners of the track delayed the start, threatening to cancel the race if the guilty party did not come forward. 

Roberts has admitted several times over the years that he was the guilty party.
Ends