Waiting for Pregnant Pause to free up we decided to walk along and do Dust in the Wind. I led up and noting the Rockfax description of crumbly rock took my time and picked my way carefully up. Even so minor rockfall (pebbles etc) occurred, each time accompanied by the obligatory shout of Rock. The route looks chossy, and is in places but has surprisingly cleaned up in others. Reached the top, set anchors and descended. Second went up on top rope and near the top dislodged a large fist sized rock along with a number of pebbles etc, shouted rock. I watched the rock plummet down directly onto someone walking underneath the route on the narrow path. Luckily the person had heard the shout and had crouched down, even so the rock struck them on the shoulder, albeit luckily being deflected slightly by the large pack being worn at the time. Once second had descended we went over to the person and administered first aid and made sure they were ok. The injury was already presenting with a substantial bruise with a large hole where the rock had pierced the skin. We applied liquid bandage to stem the bleeding, all of us were wearing helmets and commented on how had it struck a few inches higher then the outcome could have been much worse, even with the helmets. Even so and looking around there were many climbers without helmets nearby (madness!) Injured party then walked out with help of a friend and hopefully sought medical attention to check for broken bones etc (hope you're ok if reading this).