Escape in little jumper that's picked up (4)
I believe the answer is:
flee
'escape' is the definition.
(I know that escape is a more specific form of the action flee)
'little jumper that's picked up' is the wordplay.
'little jumper' becomes 'flea' (insect that jumps).
'that's picked up' shows a homophone (sound like).
'flea' sounds like 'FLEE'.
'in' is the link.
(Other definitions for flee that I've seen before include "Leave" , "Do a runner" , "retreat" , "Turn tail" , "Abscond" .)