Supporter without masculine traits opening up (7)
I believe the answer is:
telamon
'supporter' is the definition.
(I have seen 'male supporter' mean 'telamon' so perhaps 'supporter' could also mean 'telamon')
'without masculine traits opening up' is the wordplay.
'without' becomes 'no' ().
'masculine' becomes 'male' (similar in meaning).
'opening' indicates taking the first letters.
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
The initial letter of 'traits' is 't'.
'no'+'male'+'t'='nomalet'
'nomalet' backwards is 'TELAMON'.
(Other definitions for telamon that I've seen before include "supporting pillar in the shape of a man" , "male supporter" , "Column" , "Atlas" .)