this video Aaron Nace from Phlearn demonstrates how to add motion blur for images with some movement in them.
The process here is pretty simple – you start by removing the subject from the background – just duplicate the background and use the spot healing brush to remove your subject. Convert the new layer to a smart object and now add motion blur to that clean layer (a path blur will also work in more complex cases).
The next step will be to use a layer mask to bring our subject back into the image. This can be very simple if you reduce the opacity of the new layer a bit so you can see the subject that you just removed. By adding a layer mask and painting black on your subject you re-introduce the subject (do this with a soft brush).
You can clean it up later on with some white brush but basically this is all to this – very simple and easy.