Brag about amateur's support (8)
I believe the answer is:
baluster
'support' is the definition.
(baluster is a kind of support)
'brag about amateur's' is the wordplay.
'brag' becomes 'bluster' ('bluster' can be a synonym of 'brag').
'about' indicates putting letters inside.
'amateur' becomes 'a'.
'bluster' going around 'a' is 'BALUSTER'.
(Other definitions for baluster that I've seen before include "Rail hold-up" , "column" , "This could hold up rail" , "post" , "Set of posts supporting a rail" .)