The pilot reported that he had been landing and departing from the grass strip numerous times earlier in the day. For the accident flight, he was attempting to perform a midfield takeoff. During the departure roll, the airplane momentarily became airborne and then settled back into the wet grass and slowed. He opted to immediately abort the takeoff by retarding the throttle control and applying brakes. The airplane slid off the end of the grass strip and collided with a ditch, incurring damage to the right wing and tail. The pilot reported no pre impact mechanical malfunctions or failures with the airframe or engine.