Unfortunate panic had imposed disadvantage (8)
I believe the answer is:
handicap
'imposed disadvantage' is the definition.
(as in golf)
'unfortunate panic had' is the wordplay.
'unfortunate' indicates an anagram.
'panic'+'had'='panichad'
'panichad' with letters rearranged gives 'HANDICAP'.
(Other definitions for handicap that I've seen before include "Obstacle" , "Physical or mental disability, sometimes imposed" , "It impedes or hinders" , "Grand National for example" , "Circumstance that makes success difficult" .)