Operator was attempting to load his pontoon boat onto the trailer.  Operator over accelerated causing the bow of the pontoon boat to strike the trailer stop bumper on front of the trailer.  injured was standing on the trailer tongue.  Subject was struck by the stop bumper and knocked backwards into the van, breaking the rear window with the back of his head.  Subject was transported to St Al's Nampa by Canyon paramedics with cuts to the back of his left arm.
Nampa                         