I'd have called the police and reported it as attempted murder. If they later downgraded it to assault with a deadly weapon, or even simple assault, fine. However, it would have gotten them there FAST and there would be a nice paper trail.
It also would have resulted in immediate media response. Nothing much at the fair screams news story like "Fair Board member's husband investigated for alleged attempted murder of 4-H member's father" or "Fair official goes on alleged backhoe rampage at fair!"