Sharp pull (4)
(Other definitions for jerk that I've seen before include "Yank; preserve (beef)" , "dull person" , "fool" , "Sudden pull" , "Pull suddenly - twerp!" .)
(Other definitions for yank that I've seen before include "Pull roughly" , "Pull with a sudden movement" , "American from the North" , "Pull sharply" , "sudden 24D [DRAW] ?" .)