Being at the wrong place at the wrong time, you could also end upon a heap of wood for having red hair or a nasty cat in your garden. Social-economic hatred is likely always a motive to commit crimes but it is possible as you say that this motive could articulate especially well when the public order break down or when economic and social change took place. Ironically, you can observe that the more the medieval society changes in the 13th/14th centurty into an early modern society, where legal matters start to be more formlized and less bound to a person, the situation for protected minorities, including the jews, declines.