We did Rockers Revenge on Avon today and went to ab off the tree on the slab as per guidebook. It looked a bit suspect with quite a few dead branches so we looked around and there is now a two bolt lower off (close to the abb tree) at the back of the slab. So we abbed of this. My mate went first. The 2 glue in staples line up straight down the slab rather than over the edge. So it is pretty much useless to get a direct abseil down. He got to the bottom of the slab, went over the edge, probably 15m out of direct descent line and took a big swing back and hit the rock hard. He thought he had broken his collarbone, however he got down safely. I followed unaware of his accident but aware of the possibility and went over the edge much earlier to prevent a swing. I got down safely. I later had a message exchange with Ben Darby, local crag rep. and he explained there is another bolt lower off at the bottom of the slab in direct line with the one we used. So safe descent requires 2 abseils. We didn't spot the 2nd belay point. The injury resulting from the swing were torn ligaments, around shoulder.