Xavien Howard is firing back at his accuser in new court documents, obtained by TMZ Sports ... calling the woman "a scorned ex-lover" -- and insisting her STD lawsuit against him is "the epitome of a shakedown."
The Miami Dolphins star filed the docs on Friday -- one day after the woman, who filed her suit anonymously as Jane Doe, claimed he negligently gave her genital herpes.
In the documents, Howard argued the woman's suit should be thrown out ... and he says the woman has stalked him, threatened him with violence, and tried to extort him for cash.