Hitting it with a hammer is not recommended

. Most likely the dist shaft has rusted and its just "stuck". Try turning it clockwise and counter clockwise while at the same time pulling up on it. Didnt work?
Use a pair of channel lock (slip joint) plyers to crush the plastic rotor and take it off in pieces. Make sure to get all the little pieces of plastic outta the reluctor ring/magnets too.
HTH..