Pickpocket to go down briefly (3)
I believe the answer is:
dip
This clue is a double definition.
'pickpocket' is the first definition.
(I've seen this before)
'to go down briefly' is the second definition.
(Other definitions for dip that I've seen before include "Depression in a surface" , "An informal swim or a downward slope" , "Lower into water for short swim" , "An informal swim or a depression" , "Pickpocket's" .)