Twice. Both on the same high school XC course. First time was on a large downhill, clipped a rock and went down face first. This downhill followed a huge uphill, and my legs were toast at that point. 2nd time was actually at the top of that uphill. Pouring rain and spikes weren't allowed. Made the mistake of looking over at my coach to get my place, since it was our class meet, and immediately slipped and went down.