Pole on line for bird (7)
I believe the answer is:
'bird' is the definition.
(sparrow is a kind of bird)
'pole on line' is the wordplay.
'pole' becomes 'spar' (spar is a kind of pole).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'line' becomes 'row' (a row or line of things).
'for' acts as a link.
(Other definitions for sparrow that I've seen before include "one on the wing" , "Little brown bird" , "(Formerly very) common British bird" , "A chirrupy city bird" , "Small brownish bird" .)