The Vermont man charged with driving a tractor over seven police vehicles and crushing them has been found incompetent to stand trial. Roger Pion of Newport had already been involuntarily committed to the custody of the state commissioner of mental health. He has been at Fletcher Allen Health Care. Pion, 34, had faced multiple criminal counts after police said he drove his father’s tractor over six cruisers and a van at the county sheriff’s department in Derby in August, causing about $300,000 in damage. Police said he was angry over a previous arrest for marijuana possession.