Frisk entered English in the 1500s, probably from a German word that meant fresh and lively. Over time, the meaning not only evolved, it picked up speed, as it became a verb that meant to move lively, briskly. If you were frisky, you might even be dancing. By the 18th century, the sense of quick and lively movement was extended in slang to the manual dexterity exhibited by the pickpocket, whose quick hands danced deceitfully in and out of his victim’s pockets. At the same time, the police, with different motives, were said to be doing something similar when they nabbed and searched, or frisked a suspect.
Source: www.word-detective.com
