Success by American boxing amateur offers a break (6)
I believe the answer is:
hiatus
'a break' is the definition.
(hiatus is a kind of break)
'success by american boxing amateur' is the wordplay.
'success' becomes 'hit' (hit is a kind of success**).
'by' is a charade indicator (letters next to each other).
'american' becomes 'us'.
'boxing' is an insertion indicator ('box' can mean contain, as in to put in a box).
'amateur' becomes 'a'.
'hit'+'us'='hitus'
'hitus' enclosing 'a' is 'HIATUS'.
'offers' is the link.
(Other definitions for hiatus that I've seen before include "Gap, interruption" , "A break or gap in series or sequence" , "Break -- respite" , "A gap or pause in the middle" , "A lacuna or interruption" .)