Green’s Dictionary of Slang

fanning n.

[fan v.1 (1)]

1. [mid-19C–1940s] a beating, a thrashing.

2. [1900s–40s] (US Und.) a pickpocket’s preliminary running of their hands over a victim to find a wallet or bankroll.

3. [1930s] a search of a person, usu. for weapons.