Start support for young bird (7)
I believe the answer is:
gosling
'young bird' is the definition.
(I've seen this before)
'start support' is the wordplay.
'start' becomes 'go' (synonyms).
'support' becomes 'sling' (sling is a type of support for member (ie an arm)).
'go'+'sling'='GOSLING'
'for' is the link.
(Other definitions for gosling that I've seen before include "Young goose" , "Young waterbird" , "Little bird" , "Young bird" .)