Attitude of man, extremely capable (6)
I believe the answer is:
stance
'attitude' is the definition.
(I know that stance is a type of attitude)
'man extremely capable' is the wordplay.
'man' becomes 'stan' ().
'extremely' suggests removing the centre (letters on the extremes of the word are used).
'capable' with its centre taken out is 'ce'.
'stan'+'ce'='STANCE'
'of' is the link.
(Other definitions for stance that I've seen before include "Batsman's position" , "Posture - attitude" , "Attitude (of body, mind)" , "Position assumed by upright person" , "Attitude or way of standing" .)