Hines Ward -- Cops Arrest Man for Blackmailing NFL Star

Hines Ward was the target in a diabolical extortion plot ... so say police who arrested a man for allegedly threatening to release evidence that Ward paid women for sex.

Cops in Pennsylvania arrested 26-year-old Josh Van Auker yesterday ... after he allegedly demanded $15,000 from the former Pittsburgh Steelers superstar in exchange for materials that he claims would prove Hines patronized prostitutes.

According to police, Van Auker claimed Ward used to bang his GF -- though it's unclear if she is one of the people he claims Ward paid to have sex with.

Cops say they arrested Van Auker in a sting operation -- in which he made the cash-for-evidence handoff with Ward's personal assistant ... who was working with detectives.