Put out leg to trap bird in port (7)
I believe the answer is:
kowloon
'port' is the definition.
(port in Hong Kong)
'put out leg to trap bird in' is the wordplay.
'put out' becomes 'ko' (abbreviation for knock out).
'leg' becomes 'on' (cricket term, fielding positions).
'to trap' means one lot of letters goes inside another.
'bird in' becomes 'owl' (owl is a kind of bird. I am not sure about the 'in' bit.).
'ko'+'on'='koon'
'koon' placed around 'owl' is 'KOWLOON'.
(Other definitions for kowloon that I've seen before include "eastern peninsula" , "Port of Hong Kong" , "Peninsula of Hong Kong" .)