Start with support for member, developing flier (7)
I believe the answer is:
gosling
'developing flier' is the definition.
(gosling is a young goose)
'start with support for member' is the wordplay.
'start' becomes 'go' (synonyms).
'with' is a charade indicator (letters next to each other).
'support for member' becomes 'sling' (support for an injured arm).
'go'+'sling'='GOSLING'
(Other definitions for gosling that I've seen before include "Young waterbird" , "Young goose" , "Little bird" , "Young bird" .)