Run away when left in charge (4)
I believe the answer is:
flee
'run away' is the definition.
(to flee is to run away)
'left in charge' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in' means one lot of letters goes inside another.
'charge' becomes 'fee' (fee is a kind of charge).
'l' going inside 'fee' is 'FLEE'.
'when' is the link.
(Other definitions for flee that I've seen before include "Leave" , "rush" , "Do a runner" , "Abscond" , "Run quickly away" .)