The term "rising action" is a term which only has application to a critical device called Freytag's Pyramid, in which it refers to the action in Act 2 of a typical five-act play, and by "typical" I here mean a Shakespearean Tragedy, since the Freytag Pyramid doesn't always fit the histories and comedies. Since the Prologue of Romeo and Juliet is not a five-act play (it is in fact a Sonnet), the Freytag Pyramid and therefore the term "rising action" cannot apply to it. You could probably see that coming when you heard it was a prologue, since there is never any action of any kind in a Prologue (if there were, it would be an "Induction", as in The Taming of the Shrew).