Small falcon among quickest released (7)
I believe the answer is:
kestrel
'small falcon' is the definition.
(type of falcon)
'among quickest released' is the wordplay.
'among' indicates the answer is hidden within the clue.
'KESTREL' is hidden in the letters of 'quickest released'.
(Other definitions for kestrel that I've seen before include "High flier" , "It takes mice" , "Falcon that hovers" , "Small type of falcon" , "Falco tinnuculus" .)