I was working a very steep 8a sport route on lead. My belayer was wearing a helmet in case of loose rock. I was not because the route was so steep. We are both highly experienced. I had a bolt clipped a little above and to the side of me and was trying to move one metre left. I fell off a move and was instantly spinning rapidly. I had to pull my head in and put a hand out to stop my head from slamming into the rock.