Challenge not extremely skilful (9)
I believe the answer is:
competent
'skilful' is the definition.
(synonyms)
'challenge not extremely' is the wordplay.
'challenge' becomes 'compete' (to compete against someone is to challenge them).
'extremely' suggests removing the centre (only the extremes of the word are used).
'not' with its centre taken out is 'nt'.
'compete'+'nt'='COMPETENT'
(Other definitions for competent that I've seen before include ""not bad"" , "Efficient, capable" , "Expert" , "Qualified" , "Teen drink" .)