At 8:15 a.m. last Thursday, a pickup truck sideswiped a 19-year-old skateboarder on Accabonac Road in East Hampton and drove away.The skateboarder, Darian D. Donegal of East Hampton, told police he was near the Floyd Street intersection of Accabonac when a black truck struck him as it was turning right. The truck continued south on Accabonac Road, he said.There were no witnesses. Mr. Donegal, who was not wearing a helmet, complained of pain in his left elbow but refused medical attention. Anyone with information about the accident has been asked to call police at 537-7575; all calls will be kept confidential.Another recent hit-and-run involved a pedestrian, Melissa Gibbs, 56, of Armonk, N.Y., who was standing on the grassy shoulder of Old Montauk Highway in Montauk, across from the Briny Breezes Motel, when a black Range Rover Sport struck her. That accident happened on July 5 at around 5:20 p.m.The Range Rover drove off, leaving behind a piece of its passenger-side mirror. Ms. Gibbs was transported by ambulance to Southampton Hospital, where she was released after treatment.At about 9 the next morning an officer spotted a vehicle matching the description of the Range Rover, with a damaged passenger-side mirror and scratches along the passenger side, parked in a driveway on Old Montauk Highway. Later that day police arrested its owner, Casey P. Bergen of New York City, 30. He was processed at headquarters and released on a court appearance ticket, with a return date of Aug. 9.