Bird caught, when very careful (9)
I believe the answer is:
cassowary
'bird' is the definition.
(cassowary is a kind of bird)
'caught when very careful' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'when' becomes 'as' (eg 'when I walked' means 'as I walked').
'very' becomes 'so' (both can mean 'extremely').
'careful' becomes 'wary' (similar in meaning).
'c'+'as'+'so'+'wary'='CASSOWARY'
(Other definitions for cassowary that I've seen before include "So a cry was changed of the running bird" , "Large black flightless bird of N Australia" , "Winger" , "Flightless bird related to the emu - Oscar's way (anag)" , "Large flightless bird - Oscar's way (anag)" .)