A northern Iowa father and son accused of trying to run over the Nora Springs police chief with a minivan and a combine have pleaded innocent. Forty-two-year-old Virgil Fett and his 23-year-old son, Billy, both of Nora Springs, entered a written plea yesterday in Cerro Gordo County Magistrate Court. No trial date was set. Virgil Fett is charged with assaulting a peace officer and criminal mischief. Billy Fett is charged with assaulting a peace officer and interference with official acts. The charges stem from an incident earlier this month with Police Chief Alex Leu, who was investigating a complaint of reckless driving against the Fetts. The Fetts allegedly tried to run over Leu with a van and the combine when they were confronted in a field they were harvesting.