Lack of ability in role (10)
I believe the answer is:
incapacity
'lack of ability' is the definition.
(being incapable)
'in role' is the wordplay.
'role' becomes 'capacity' (I've seen this in another clue).
'in'+'capacity'='INCAPACITY'
(Other definitions for incapacity that I've seen before include "Lack of authority" , "Helplessness" , "Lack of required skills" , "Powerlessness" , "Lack of power or ability" .)