Be unsteady, being sick during leave (9)
I believe the answer is:
vacillate
'be unsteady' is the definition.
(I've seen this before)
'sick during leave' is the wordplay.
'sick' becomes 'ill' (similar in meaning).
'during' indicates putting letters inside.
'leave' becomes 'vacate' (to vacate a place is to leave it).
'ill' placed inside 'vacate' is 'VACILLATE'.
'being' acts as a link.
(Other definitions for vacillate that I've seen before include "Hesitate" , "Keep changing one's mind" , "Shilly-shally" , "Be in two minds" , "Be irresolute" .)