To compact down, a quite narrow run of gravel, on my drive, I decided my sds set to roto-stop, just hammer, was perfect. I welded a bit of bar, to the end of a sds chisel bit, and set to work compacting. It worked well, I took a break, to admire my work, then restarted - except I'd accidentally caught the roto-stop switch, the bar swung round at high speed and clouted my ankle bone. The pain was tremendous and was sore for days afterwards..
Ouch...