Leave hastily, a fugitive (7)
I believe the answer is:
runaway
'a fugitive' is the definition.
(I know that fugitive can be written as runaway)
'leave hastily' is the wordplay.
'leave' becomes 'run' (running is a kind of leaving).
'hastily' becomes 'away' (I am not sure about this - if you are sure you should believe this answer much more).
'run'+'away'='RUNAWAY'
Can you help me to learn more?
(Other definitions for runaway that I've seen before include "One who has taken flight" , "Absconder" , "refugee?" , "One who flies" , "scooter?" .)