Nipper close to mother in Hackney, perhaps (4)
I believe the answer is:
crab
'nipper' is the definition.
(I have seen 'Nautical nipper' mean 'crab' so perhaps 'nipper' could also mean 'crab')
'close to mother in hackney perhaps' is the wordplay.
'close to' indicates one should take the final letters (the close of something is the end).
'in' is an insertion indicator.
'hackney perhaps' becomes 'cab' (I can't justify this - if you can you should give a lot more credence to this answer).
The last letter of 'mother' is 'r'.
'r' placed within 'cab' is 'CRAB'.
Can you help me to learn more?
(Other definitions for crab that I've seen before include "Sour character" , "Sourpuss < to wreck" , "move obliquely" , "Marine crustacean (seen on 1 across?)" , "Clawed crustacean" .)