It was a fancy dress jumping competition. He didn't have a costume so the organisers told him to do it naked - they didn't think he would go through with it!
OMG, have to say blinking good rider, dont think my seat is that good fully clothed and a saddle.
Also nearly a clear round, would of been funny if he had won and someone had to present to him, you would not be able to help looking in THAT direction.