>>1021671So the hanger, the part that of the frame (possibly separate from the actual dropout) that the derailer bolts onto, is round instead of having that small protrusion at the bottom? If so you'll need to buy a new hanger if it's separate, or get it welded if it's part of the dropout.
There are two ways I can see it happening. One would be for the derailer to be forced so hard that it rounds it off which would almost certainly also destroy the derailer, the second would be from sitting the frame on a concrete floor on the hanger (so with the wheel and derailer removed) multiple times over a long period (or just sliding it along the ground).
